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 A145043 #7 Jul 22 2025 06:12:28
%S A145043 5,17,23,47,53,71,73,127,173,233,251,269,281,347,353,359,431,487,491,
%T A145043 509,541,563,569,593,613,677,743,773,827,857,863,883,929,953,977,1013,
%U A145043 1153,1187,1283,1319,1361,1373,1439,1481,1583,1613,1619,1709,1871,1997
%N A145043 Primes p for which s=2 is the least positive integer such that sp-t(sp) is a triangular number, where t(n) is the maximal triangular number not exceeding n.
%o A145043 (PARI) maxt(n) = {k = 1; while ((t=k*(k+1)/2) < n, k++); if (t == n, t, k--; k*(k+1)/2);}
%o A145043 lista(nn) = {forprime(p = 2, nn, if (! ispolygonal(p - maxt(p), 3) && ispolygonal(2*p - maxt(2*p), 3), print1(p, ", ");););} \\ _Michel Marcus_, Jul 25 2014
%Y A145043 Cf. A000217, A145032, A145016, A145022, A145023.
%K A145043 nonn
%O A145043 1,1
%A A145043 _Vladimir Shevelev_, Sep 30 2008
%E A145043 More terms from _Michel Marcus_, Jul 25 2014