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- #!/usr/bin/ruby
- # a(n) is the smallest n-gonal pyramidal number with exactly n distinct prime factors.
- # https://oeis.org/A358864
- # Known terms:
- # 84, 1785, 299880, 1020510, 8897460, 102612510, 33367223274, 249417828660, 9177835927260, 10064864238489060, 5558913993302670, 15633689593760207970, 3792821921183752657200
- # PARI/GP program:
- /*
- a(n) = if(n<3, return()); for(k=1, oo, my(t=(k*(k+1)*((n-2)*k + (5-n)))\6); if(omega(t) == n, return(t))); \\ ~~~~
- */
- func a(n) {
- for k in (1..Inf) {
- if (pyramidal(k, n).is_omega_prime(n)) {
- return pyramidal(k, n)
- }
- }
- }
- for n in (3..100) {
- say "a(#{n}) = #{a(n)}"
- }
- __END__
- a(12) = 10064864238489060
- a(13) = 5558913993302670
- a(14) = 15633689593760207970
- a(15) = 3792821921183752657200
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