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- #!/usr/bin/ruby
- # a(n) = Number of distinct prime factors of sigma(sigma_n(n)).
- # https://oeis.org/A??????
- # Number of distinct prime factors of A347718(n).
- # See also:
- # https://oeis.org/A347718
- # First terms of the sequence:
- # 0, 2, 2, 2, 3, 5, 4, 5, 6, 6, 5, 8, 5, 7, 10, 5, 4, 11, 9, 12, 10, 9, 12, 13, 10, 10, 12, 16, 12, 18, 17, 12, 15, 16, 16, 14, 13, 11, 17, 20, 11, 21, 15, 17, 20, 17, 23, 19, 14, 26, 22, 27, 21, 25, 25, 21, 25, 14, 16, 29, 13, 15, 24, 22, 24, 25, 23, 25, 29, 28, 18, 33
- include("../../../factordb/auto.sf")
- #sigma_factors_symbolic(sigma(118, 118)).each { .say }
- func a(n) {
- #sigma(sigma(n, n))
- var f = sigma_factors(sigma(n, n))
- #var f = sigma_factors_symbolic(n, n)
- f.map { FF_factordb(_) }.flat.uniq.len
- }
- for n in (Num(ARGV[0] \\ 1) .. 1000) {
- #print(a(n), ", ")
- say "#{n} #{a(n)}"
- }
- __END__
- # PARI/GP program:
- a(n) = omega(sigma(sigma(n, n)));
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