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 A364798 #9 Aug 12 2023 01:17:22
%S A364798 1,3,6,78,448516225,448254714630193471
%N A364798 Triangular numbers that for some k >= 1 are also the sum of the first k noncomposite numbers (1 together with the primes).
%C A364798 a(n) = A000217(i) = A014284(j) for appropriate i, j.
%e A364798 78 is a term because 78 = 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 + 11 + 12 = 1 + 2 + 3 + 5 + 7 + 11 + 13 + 17 + 19.
%t A364798 Select[Accumulate[Join[{1}, Prime[Range[10000]]]], IntegerQ[Sqrt[8 # + 1]] &]
%Y A364798 Intersection of A000217 and A014284.
%Y A364798 Cf. A008578, A066527, A110996, A364799.
%K A364798 nonn,more
%O A364798 1,2
%A A364798 _Ilya Gutkovskiy_, Aug 08 2023
%E A364798 a(6) from _Jinyuan Wang_, Aug 09 2023