A364610 Centered pentagonal numbers which are products of three distinct primes.

1266, 1626, 2806, 3706, 4731, 6126, 7426, 7701, 9766, 10726, 13506, 15801, 18706, 19581, 25251, 26266, 26781, 31641, 35106, 36906, 40006, 50766, 52926, 56626, 57381, 62806, 69306, 71826, 74391, 76126, 85101, 90726, 93606, 95551, 96531, 99501, 106606, 108681, 109726, 117181, 121551, 123766

Offset

1,1

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Example

A005891(22) = 1266 = (5*22^2 + 5*22 + 2)/2 = 2 * 3 * 211.
A005891(25) = 1626 = (5*25^2 + 5*25 + 2)/2 = 2 * 3 * 271.
A005891(33) = 2806 = (5*33^2 + 5*33 + 2)/2 = 2 * 23 * 61.

Maple

select(t -> ifactors(t)[2][.., 2] = [1, 1, 1], [seq(5*n*(n + 1)/2 + 1, n=1..1000)]); # Robert Israel, Jul 10 2026

Mathematica

Select[Table[5*n*(n + 1)/2 + 1, {n, 0, 225}], FactorInteger[#][[;; , 2]] == {1, 1, 1} &] (* Amiram Eldar, Sep 07 2023 *)

Crossrefs

Intersection of A005891 and A007304.

Sequence in context: A233887 A234147 A252562 * A038652 A204720 A204959

Adjacent sequences: A364607 A364608 A364609 * A364611 A364612 A364613

Keyword

nonn,changed

Author

Massimo Kofler, Sep 07 2023

Status

approved