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 A336263 #23 Sep 08 2020 03:37:24 %S A336263 13,22,31,37,40,49,52,58,62,67,73,76,82,85,87,94,97,103,112,115,121, %T A336263 122,127,130,136,137,139,142,148,157,162,166,171,172,175,178,181,184, %U A336263 187,192,193,199,202,211,212,214,217,220,227,229,232,237,238,241,247,253,256 %N A336263 Numbers of the form k + s + 2*k*s where k is a positive integer and s is a Sundaram number (A159919). %C A336263 Numbers k such that bigomega(2*k + 1) >= 3. - _David A. Corneth_, Jul 15 2020 %C A336263 If a term s in A159919 is not here, 2*s+1 is a semiprime. %e A336263 4 is a Sundaram number, therefore 1+4+2*4*1=13 is a term, and (13*2)+1=27 is not a semiprime. %t A336263 Select[Range[2^8], PrimeOmega[2*# + 1] >= 3 &] (* _Amiram Eldar_, Jul 15 2020 *) %o A336263 (PARI) is(n) = bigomega(2*n + 1) >= 3 \\ _David A. Corneth_, Jul 15 2020 %Y A336263 Cf. A001222, A159919. %K A336263 nonn,easy %O A336263 1,1 %A A336263 _Davide Rotondo_, Jul 15 2020 %E A336263 More terms from _David A. Corneth_, Jul 15 2020