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

Author

Massimo Kofler, Jan 29 2023

Keywords

• nonn

Examples

			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.
		

Links

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

Crossrefs

Intersection of A069099 and A007304.

Programs

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 *)