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 A298270 #33 Apr 20 2024 11:10:12
%S A298270 0,10,78,153,946,177310,450775,13595505,150988753,4478601403,
%T A298270 5409300078,5589152128,76060335351,248156250265,1793751529485,
%U A298270 176149383165876,187718592284301,233626949305596,11362376565228270,18886935830647605,1943937379018997076
%N A298270 Triangular numbers that for some k are also the sum of the first k composites.
%e A298270 10 is a term because 10 = 1 + 2 + 3 + 4 = 4 + 6.
%t A298270 Join[{0},Select[Accumulate[Select[Range[10^6],CompositeQ]],OddQ[Sqrt[8#+1]]&]] (* The program generates the first 14 terms of the sequence. *) (* _Harvey P. Dale_, Apr 20 2024 *)
%o A298270 (PARI) lista(nn) = {my(s=0); forcomposite(n=0, nn, if(ispolygonal(s, 3), print1(s, ", ")); s += n; ); } \\ after _Michel Marcus_ at A053767
%Y A298270 Intersection of A000217 and A053767.
%Y A298270 Cf. A066527, A154587, A294174.
%K A298270 nonn
%O A298270 1,2
%A A298270 _Altug Alkan_, Feb 15 2018