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 A339480 #9 May 28 2021 17:50:58 %S A339480 337,577,1249,1567,2047,2887,3697,4231,4417,6727,6961,7199,7441,7687, %T A339480 8977,10081,10367,10657,11857,12799,14449,15487,16927,17297,17671, %U A339480 20401,20807,21217,21631,22897,23327,23761,24199,27847,29767,30257,30751,32257,33799,35377,37537,40897 %N A339480 Numbers of the form (k^2 - 2) / 2 where k - 1 and k + 1 are both odd composite numbers. %F A339480 a(n) = (A129820(2*n - 1) * A129820(2*n) - 1) / 2. %e A339480 For k = 26, k - 1 = 25 and k + 1 = 27 are both odd composite numbers. So (26^2 - 2) / 2 = 337 is a term of the sequence. %o A339480 (PARI) k = 1; forcomposite(c = 1, 287, if(c%2 <> 0, if(c-k == 2, print1((c * (c - 2) - 1) / 2", ")); k = c)) %Y A339480 Cf. A071904, A129820. %K A339480 nonn %O A339480 1,1 %A A339480 _Dimitris Valianatos_, Apr 24 2021