A359017 a(n) is the index of the smallest triangular number with exactly n distinct prime factors.

1, 2, 3, 11, 20, 84, 455, 1364, 10659, 58695, 254540, 728364, 13516580, 133595384, 812646120, 5327923964, 68971338435, 838101203939, 7588384207404, 69322940121435, 490005293940084

Offset

0,2

Links

Table of n, a(n) for n=0..20.

Eric Weisstein's World of Mathematics, Distinct Prime Factors

Eric Weisstein's World of Mathematics, Triangular Number

Prog

(PARI) a(n) = my(k=1); while(omega(k*(k+1)/2) != n, k++); k; \\ Michel Marcus, Feb 26 2023

Crossrefs

Cf. A000217, A001221, A076550, A076551.

Sequence in context: A004687 A097895 A298351 * A023182 A302310 A295958

Adjacent sequences: A359014 A359015 A359016 * A359018 A359019 A359020

Keyword

nonn,more

Author

Ilya Gutkovskiy, Dec 12 2022

Extensions

a(19)-a(20) from Michael S. Branicky, Feb 25 2023

Status

approved