A360183 - OEIS

%I #27 Aug 12 2023 14:55:38

%S 638,4922,6322,11978,15478,16906,19426,21022,23822,25586,28666,35351,

%T 39698,48322,53383,55126,70078,80333,83546,92422,98197,105358,107801,

%U 132406,147806,156563,162541,171718,182743,209231,210946,233878,248578,263726,269522,281303

%N Centered heptagonal numbers which are sphenic numbers.

%H Robert Israel, <a href="/A360183/b360183.txt">Table of n, a(n) for n = 1..10000</a>

%e A069099(14) =  638 = (7*14^2 - 7*14 + 2)/2 = 2 * 11 * 29.

%e A069099(38) = 4922 = (7*38^2 - 7*38 + 2)/2 = 2 * 23 * 107.

%e A069099(43) = 6322 = (7*43^2 - 7*43 + 2)/2 = 2 * 29 * 109.

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

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

%Y Intersection of A069099 and A007304.

%K nonn

%O 1,1

%A _Massimo Kofler_, Jan 29 2023