A360183 Centered heptagonal numbers which are sphenic numbers.

638, 4922, 6322, 11978, 15478, 16906, 19426, 21022, 23822, 25586, 28666, 35351, 39698, 48322, 53383, 55126, 70078, 80333, 83546, 92422, 98197, 105358, 107801, 132406, 147806, 156563, 162541, 171718, 182743, 209231, 210946, 233878, 248578, 263726, 269522, 281303

Offset

1,1

Links

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

Example

A069099(14) =  638 = (7*14^2 - 7*14 + 2)/2 = 2 * 11 * 29.
A069099(38) = 4922 = (7*38^2 - 7*38 + 2)/2 = 2 * 23 * 107.
A069099(43) = 6322 = (7*43^2 - 7*43 + 2)/2 = 2 * 29 * 109.

Maple

select(t -> ifactors(t)[2][.., 2]=[1, 1, 1], [(7*i^2-7*i+2)/2 $ i=1..1000]); # Robert Israel, Feb 28 2023

Mathematica

Select[Table[(7*n^2 - 7*n + 2)/2, {n, 1, 300}], FactorInteger[#][[;; , 2]] == {1, 1, 1} &] (* Amiram Eldar, Jan 29 2023 *)

Crossrefs

Intersection of A069099 and A007304.

Sequence in context: A212399 A264449 A210883 * A281884 A200710 A250661

Adjacent sequences: A360180 A360181 A360182 * A360184 A360185 A360186

Keyword

nonn

Author

Massimo Kofler, Jan 29 2023

Status

approved