This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A381960 #9 Mar 18 2025 15:56:11
%S A381960 22,106,253,386,841,1198,1618,2101,2458,3046,3473,4166,4411,5461,6623,
%T A381960 6931,7246,7897,8926,9647,10018,12811,13238,14113,15947,16423,17893,
%U A381960 19951,22121,22681,24403,24991,26797,27413,30598,31921,32593,33958,38221,40447,41966,43513
%N A381960 Centered heptagonal numbers which are semiprime.
%e A381960 A069099(3) = 22 = 21*(3-1)/2 + 1 = 2*11.
%e A381960 A069099(6) = 106 = 42*(6-1)/2 + 1 = 2*53.
%e A381960 A069099(9) = 253 = 63*(9-1)/2 + 1 = 11*23.
%t A381960 Select[Table[(7*n^2 - 7*n + 2)/2, {n, 1, 120}], PrimeOmega[#] == 2 &] (* _Amiram Eldar_, Mar 11 2025 *)
%o A381960 (PARI) select(x->bigomega(x)==2, vector(120, n, (7*n^2-7*n+2)/2)) \\ _Michel Marcus_, Mar 11 2025
%Y A381960 Intersection of A069099 and A001358.
%Y A381960 Cf. A360183.
%K A381960 nonn
%O A381960 1,1
%A A381960 _Massimo Kofler_, Mar 11 2025