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- #!/usr/bin/ruby
- # a(n) is the index of the smallest tribonacci number (A000073) with exactly n prime factors (counted with multiplicity).
- # https://oeis.org/A359878
- # Known terms:
- # 2, 4, 5, 9, 8, 17, 13, 52, 16, 40, 36, 32, 62, 88, 96, 144, 112
- # a(22) > 464.
- # a(23) > 464.
- include("../../../factordb/auto.sf")
- func a(n, from=1) {
- for k in (from..Inf) {
- var t = fib(k,3)
- say "[#{n},#{k}] Checking: #{t}"
- if (try { bigomega(t) == n } catch { t.is_almost_prime(n) }) {
- #if (t.is_almost_prime(n)) {
- return k
- }
- }
- }
- say a(22, 465)
- #say a(23, 445)
- #~ for n in (0..100) {
- #~ say "a(#{n}) = #{a(n)}"
- #~ }
- __END__
- a(0) = 2
- a(1) = 4
- a(2) = 5
- a(3) = 9
- a(4) = 8
- a(5) = 17
- a(6) = 13
- a(7) = 52
- a(8) = 16
- a(9) = 40
- a(10) = 36
- a(11) = 32
- a(12) = 62
- a(13) = 88
- a(14) = 96
- a(15) = 144
- a(16) = 112
- a(17) = 221
- a(18) = 256
- a(19) = 208
- a(20) = 400
- a(21) = 192
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