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 A175133 #26 Oct 06 2023 12:53:49
%S A175133 3,5,217,1065,93448,39545957,240439822,1894541497,132563927578,
%T A175133 309101198255
%N A175133 Sum of first a(n) consecutive primes gives a triangular number.
%C A175133 A007504(a(n)) = A000217(j) for some j.
%C A175133 Numbers k such that Sum_{i=1..k} prime(i) = j*(j+1)/2, where prime(i) is i-th prime, and j an integer.
%e A175133 k=3 is a term: 2+3+5=10, and 10=4*5/2 is a triangular number, j=4.
%e A175133 k=5 is a term: 2+3+5+7+11=28, and 28=7*8/2 is a triangular number, j=7.
%e A175133 k=217 is a term: 2+3+...+1327=133386, and 133386=516*517/2 is a triangular number, j=516.
%o A175133 (PARI) isok(n) = ispolygonal(sum(k=1, n, prime(k)), 3); \\ _Michel Marcus_, Oct 13 2018
%Y A175133 Cf. A000040, A000217, A007504, A066527.
%Y A175133 Cf. also A033997, A364696, A366270.
%K A175133 nonn,more
%O A175133 1,1
%A A175133 _Ctibor O. Zizka_, Feb 20 2010
%E A175133 a(6)-a(10) from _Nathaniel Johnston_, May 10 2011 (a(7)-a(10) based on comments by _Donovan Johnson_)
%E A175133 Name, comment and example clarified by _Ilya Gutkovskiy_, Aug 07 2023