Sha256: 5666089c65227bea9d971a5ab2ad0da837e628a6cfa22d9647bb5dee9278ea6e
Contents?: true
Size: 496 Bytes
Versions: 15
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Stored size: 496 Bytes
Contents
# coding: utf-8
class Integer
def untouchable?
# * The first untouchable integer is 2
# * Perfect numbers are never untouchable because they can be expressed
# as the sum of their own proper divisors
# * If p is prime, the sum of the proper divisors of p**2 is p + 1;
# therefore, no untouchable number is one more than a prime.
return false if self < 2 or perfect? or (self - 1).prime?
(1..((self - 1)**2)).none? do |m|
m.σ - m == self
end
end
end
Version data entries
15 entries across 15 versions & 1 rubygems