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- #!/usr/bin/ruby
- # Number of distinct prime factors of sigma_n(n).
- # https://oeis.org/A352420
- include("../../../factordb/auto.sf")
- func a(n) {
- var f = sigma_factors(n, n)
- #var f = sigma_factors_symbolic(n, n)
- f.map { FF_factordb(_) }.flat.uniq.len
- }
- for n in (1..1000) {
- #print(a(n), ", ")
- say "#{n} #{a(n)}"
- }
- __END__
- # First 100 terms:
- 0, 1, 2, 3, 3, 4, 3, 2, 3, 5, 6, 8, 5, 5, 8, 6, 3, 8, 5, 11, 9, 7, 8, 10, 8, 8, 10, 12, 7, 13, 7, 11, 15, 10, 15, 11, 7, 8, 11, 10, 6, 14, 8, 14, 14, 11, 10, 17, 6, 21, 15, 16, 8, 18, 16, 15, 16, 6, 9, 22, 8, 10, 17, 13, 17, 17, 7, 17, 20, 17, 8, 23, 4, 13, 21, 16, 19, 21, 7, 22, 12, 8, 12, 29, 15, 8, 21, 15, 6, 32, 19, 16, 20, 12, 23, 26, 8, 19, 22, 32
- a(67)-a(75) from ~~~~
- # PARI/GP program:
- a(n) = omega(sigma(n, n));
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