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 A364799 #12 Aug 23 2023 08:35:42 %S A364799 3,15,1236378,1454365,3541791,104856921,2677839153,3656187921870, %T A364799 3973810409128,1448587865213374600,36691639282445615088081 %N A364799 Triangular numbers that for some k >= 1 are also the sum of the first k odd primes. %C A364799 a(n) = A000217(i) = A071148(j) for appropriate i, j. %e A364799 15 is a term because 15 = 1 + 2 + 3 + 4 + 5 = 3 + 5 + 7. %t A364799 Select[Accumulate[Prime[Range[2, 1000000]]], IntegerQ[Sqrt[8 # + 1]] &] %o A364799 (PARI) lista(nn) = my(s=0); forprime(p=3, nn, s+=p; if(ispolygonal(s, 3), print1(s, ", "))) \\ _Jinyuan Wang_, Aug 10 2023 %Y A364799 Intersection of A000217 and A071148. %Y A364799 Cf. A065091, A066527, A364798. %K A364799 nonn,more %O A364799 1,1 %A A364799 _Ilya Gutkovskiy_, Aug 08 2023 %E A364799 a(10) from _Jinyuan Wang_, Aug 10 2023 %E A364799 a(11) from _Martin Ehrenstein_, Aug 23 2023