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 A115708 #8 Apr 27 2022 15:22:39 %S A115708 10,15,21,22,235,287,517,529,671,1513,1555,2611,5137,5331,6241,7017, %T A115708 7171,7421,7597,7814,10078,10913,15011,15094,15214,15251,20395,20603, %U A115708 21542,23129,24501,24873,25157,26851,27161,51998,53297,54989,55551 %N A115708 Semiprimes (A001358) whose digit reversal is a pentagonal number (A000326). %H A115708 Harvey P. Dale, <a href="/A115708/b115708.txt">Table of n, a(n) for n = 1..100</a> %e A115708 235=5*47 is semiprime and 532 is the 19th pentagonal number. %t A115708 Select[Range[60000],PrimeOmega[#]==2&&IntegerQ[(1+Sqrt[1+24* IntegerReverse[#]])/ 6]&] (* _Harvey P. Dale_, Apr 27 2022 *) %Y A115708 Cf. A000326, A001358, A115709. %K A115708 nonn,base %O A115708 1,1 %A A115708 _Giovanni Resta_, Jan 31 2006