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 A117674 #17 Feb 08 2021 05:27:12
%S A117674 3,19,37,73,109,127,163,181,271,307,433,523,541,613,631,811,1009,1063,
%T A117674 1117,1153,1171,1423,1531,1621,1801,1999,2017,2053,2143,2161,2251,
%U A117674 2341,2503,2521,3061,3313,3331,3511,3889,4051,4231,4789,4969,4987,5023,5113
%N A117674 Prime numbers whose sum of digits is a triangular number.
%H A117674 Amiram Eldar, <a href="/A117674/b117674.txt">Table of n, a(n) for n = 1..10000</a>
%e A117674 1999 is in the sequence because it is a prime number and the sum of its digits 1+9+9+9 = 28 is a triangular number.
%t A117674 t={};Do[m = Total[IntegerDigits[Prime[n]]];If[IntegerQ[(Sqrt[8*m + 1]-1)/2],AppendTo[t, Prime[n]]],{n,700}];t (* _Jayanta Basu_, Apr 27 2013 *)
%o A117674 (PARI) isok(p) = isprime(p) && ispolygonal(sumdigits(p), 3); \\ _Michel Marcus_, Feb 08 2021
%Y A117674 Intersection of A000040 and A187744.
%Y A117674 Cf. A000217, A007953.
%K A117674 nonn,base
%O A117674 1,1
%A A117674 Luc Stevens (lms022(AT)yahoo.com), Apr 27 2006