40 lines
918 B
Text
40 lines
918 B
Text
using Primes
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function properdivisors(n::T) where {T<:Integer}
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0 < n || throw(ArgumentError("number to be factored must be ≥ 0, got $n"))
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1 < n || return T[]
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!isprime(n) || return T[one(T)]
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f = factor(n)
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d = T[one(T)]
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for (k, v) in f
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c = T[k^i for i in 0:v]
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d = d*c'
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d = reshape(d, length(d))
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end
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sort!(d)
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return d[1:end-1]
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end
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lo = 1
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hi = 10
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println("List the proper divisors for ", lo, " through ", hi, ".")
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for i in lo:hi
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println(@sprintf("%4d", i), " ", properdivisors(i))
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end
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hi = 2*10^4
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println("\nFind the numbers within [", lo, ",", hi, "] having the most divisors.")
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maxdiv = 0
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nlst = Int[]
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for i in lo:hi
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ndiv = length(properdivisors(i))
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if ndiv > maxdiv
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maxdiv = ndiv
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nlst = [i]
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elseif ndiv == maxdiv
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push!(nlst, i)
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end
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end
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println(nlst, " have the maximum proper divisor count of ", maxdiv, ".")
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