A359015 a(n) is the index of the smallest n-gonal pyramidal number with exactly n distinct prime factors.
7, 17, 84, 115, 220, 468, 3058, 5719, 18290, 182104, 144738, 1984619, 12051935, 41133455, 79156454
Offset: 3
Links
- Eric Weisstein's World of Mathematics, Distinct Prime Factors.
- Eric Weisstein's World of Mathematics, Pyramidal Number.
Programs
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Mathematica
p[k_, n_] := k*(k + 1)*((n - 2)*k + 5 - n)/6; a[n_] := Module[{k = 1}, While[PrimeNu[p[k, n]] != n, k++]; k]; Array[a, 11, 3] (* Amiram Eldar, Jul 03 2025 *) -
PARI
p(k, n) = k*(k + 1)*((n - 2)*k + 5 - n)/6; a(n) = {my(k = 1); while(omega(p(k, n)) != n, k++); k;} \\ Amiram Eldar, Jul 03 2025
Extensions
a(16)-a(17) from Amiram Eldar, Jul 03 2025