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 A113530 #27 Oct 09 2022 05:22:59 %S A113530 91,169,217,469,721,817,1027,1141,1261,1387,2611,2977,3781,3997,4681, %T A113530 5677,5941,6487,6769,7651,7957,8587,9577,10981,11347,12481,12871, %U A113530 14077,14491,15769,16207,17557,18019,18961,20419,20917,21421,22969,24031 %N A113530 Semiprimes in A003215. %C A113530 Intersection of A003215 and A001358. %H A113530 Michael De Vlieger, <a href="/A113530/b113530.txt">Table of n, a(n) for n = 1..10000</a> %e A113530 a(1) = 91 because A003215(5) = (5+1)^3 - 5^3 = 91 = 7 * 13 is semiprime. %e A113530 a(7) = 121 because A003215(7) = (7+1)^3 - 7^3 = 169 = 13^2 is semiprime; the two prime factors need not be distinct. %t A113530 Select[Array[3 #^2 + 3 # + 1 &, 90], PrimeOmega[#] == 2 &] (* _Michael De Vlieger_, Mar 17 2021 *) %Y A113530 Cf. A001358, A003215. %Y A113530 Cf. A113519, A113524, A113525, A113527, A113528. %K A113530 easy,nonn %O A113530 1,1 %A A113530 _Jonathan Vos Post_, Jan 12 2006