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- #!/usr/bin/ruby
- # Index of smallest Fibonacci number with n prime factors when counted with multiplicity.
- # https://oeis.org/A072396
- # Known terms:
- # 3, 8, 6, 20, 18, 12, 30, 54, 24, 36, 138, 48, 84, 72, 108, 96, 210, 120, 276, 168, 216, 252, 288, 240, 336, 570, 384, 420, 360, 576, 480, 540, 504, 660, 600, 672, 990, 720, 792, 840, 1152, 1140
- # Lower-bounds:
- # a(43) > 1452
- # 1452 < a(43) <= 1596. a(44) = 1296. a(45) = 1368. a(46) = 1080. a(47) = 1200. a(48) <= 1728.
- include("../../../factordb/auto.sf")
- func a(n, from=1) {
- for k in (from..Inf) {
- #k.is_prime && next
- var t = fib(k)
- 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(48)
- #~ for n in (1..100) {
- #~ say "a(#{n}) = #{a(n)}"
- #~ }
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