111 lines
2.9 KiB
Nim
111 lines
2.9 KiB
Nim
import bignum
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import strformat
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const SmallPrimes = [
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2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97,
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101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199,
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211, 223, 227, 229, 233, 239, 241, 251, 257, 263, 269, 271, 277, 281, 283, 293,
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307, 311, 313, 317, 331, 337, 347, 349, 353, 359, 367, 373, 379, 383, 389, 397,
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401, 409, 419, 421, 431, 433, 439, 443, 449, 457, 461, 463, 467, 479, 487, 491, 499,
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503, 509, 521, 523, 541, 547, 557, 563, 569, 571, 577, 587, 593, 599,
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601, 607, 613, 617, 619, 631, 641, 643, 647, 653, 659, 661, 673, 677, 683, 691,
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701, 709, 719, 727, 733, 739, 743, 751, 757, 761, 769, 773, 787, 797,
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809, 811, 821, 823, 827, 829, 839, 853, 857, 859, 863, 877, 881, 883, 887,
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907, 911, 919, 929, 937, 941, 947, 953, 967, 971, 977, 983, 991, 997]
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let
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One = newInt(1)
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Two = newInt(2)
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Ten = newInt(10)
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#---------------------------------------------------------------------------------------------------
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proc isPrime(n: Int): bool =
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if n < Two: return false
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for sp in SmallPrimes:
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# let spb = newInt(sp)
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if n == sp: return true
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if (n mod sp).isZero: return false
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if n < sp * sp: return true
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result = probablyPrime(n, 25) != 0
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#---------------------------------------------------------------------------------------------------
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proc cycle(n: Int): Int =
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var m = n
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var p = 1
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while m >= Ten:
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p *= 10
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m = m div 10
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result = m + Ten * (n mod p)
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#---------------------------------------------------------------------------------------------------
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proc isCircularPrime(p: Int): bool =
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if not p.isPrime(): return false
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var p2 = cycle(p)
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while p2 != p:
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if p2 < p or not p2.isPrime():
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return false
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p2 = cycle(p2)
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result = true
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#---------------------------------------------------------------------------------------------------
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proc testRepunit(digits: int) =
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var repunit = One
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var count = digits - 1
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while count > 0:
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repunit = Ten * repunit + One
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dec count
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if repunit.isPrime():
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echo fmt"R({digits}) is probably prime."
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else:
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echo fmt"R({digits}) is not prime."
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#---------------------------------------------------------------------------------------------------
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echo "First 19 circular primes:"
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var p = 2
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var line = ""
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var count = 0
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while count < 19:
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if newInt(p).isCircularPrime():
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if count > 0: line.add(", ")
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line.add($p)
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inc count
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inc p
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echo line
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echo ""
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echo "Next 4 circular primes:"
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var repunit = One
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var digits = 1
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while repunit < p:
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repunit = Ten * repunit + One
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inc digits
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line = ""
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count = 0
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while count < 4:
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if repunit.isPrime():
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if count > 0: line.add(' ')
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line.add(fmt"R({digits})")
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inc count
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repunit = Ten * repunit + One
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inc digits
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echo line
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echo ""
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testRepUnit(5003)
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testRepUnit(9887)
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testRepUnit(15073)
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testRepUnit(25031)
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testRepUnit(35317)
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testRepUnit(49081)
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