28 lines
693 B
Julia
28 lines
693 B
Julia
using Primes
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function σ(n)
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f = [one(n)]
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for (p,e) in factor(n)
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f = reduce(vcat, [f*p^j for j in 1:e], init=f)
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end
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return sum(f)
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end
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isDuffinian(n) = !isprime(n) && gcd(n, σ(n)) == 1
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function testDuffinians()
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println("First 50 Duffinian numbers:")
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foreach(p -> print(rpad(p[2], 4), p[1] % 25 == 0 ? "\n" : ""),
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enumerate(filter(isDuffinian, 2:217)))
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n, found = 2, 0
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println("\nFifteen Duffinian triplets:")
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while found < 15
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if isDuffinian(n) && isDuffinian(n + 1) && isDuffinian(n + 2)
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println(lpad(n, 6), lpad(n +1, 6), lpad(n + 2, 6))
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found += 1
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end
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n += 1
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end
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end
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testDuffinians()
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