invmod_of_coprime_factorials.sf

#!/usr/bin/ruby

# Daniel "Trizen" Șuteu
# License: GPLv3
# Date: 07 March 2017
# https://github.com/trizen

# An interesting sequence: invmod(A095996(n), n)

# For prime numbers p, a(p) = p-1.
# However, there are some composite numbers that also share this property.
# First few of those numbers, are: 1, 4, 6, 30, 36, 48, 225, 375, 390, 962, 3005, 15125, 29670, 61411

# See also:
#   https://oeis.org/A095996

func a(n) {
    var f = n!
    factor(n).each {|p| f.remove!(p) }
    invmod(f, n)
}

for n in (1..50) {
    say "a(#{n}) = #{a(n)}"
}

__END__
First 50 terms are: 0, 1, 2, 3, 4, 5, 6, 3, 4, 3, 10, 5, 12, 9, 1, 3, 16, 11, 18, 1, 13, 3, 22, 7, 1, 23, 14, 3, 28, 29, 30, 3, 20, 9, 31, 35, 36, 5, 28, 1, 40, 11, 42, 1, 7, 3, 46, 47, 36, 39