prog.sf

#!/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