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 A078724 #10 Sep 08 2022 08:45:08
%S A078724 5,7,13,23,41,61,89,127,167,223,271,347,419,491,593,677,797,911,1033,
%T A078724 1171,1303,1481,1619,1801,1999,2203,2383,2621,2803,3061,3323,3559,
%U A078724 3823,4093,4391,4679,4999,5333,5653,5987,6323,6701,7043,7489,7867,8273,8699,9127
%N A078724 a(n) = prime(n*(n+1)/2+3).
%C A078724 The sum of the reciprocals of the terms appears to converge.
%H A078724 Vincenzo Librandi, <a href="/A078724/b078724.txt">Table of n, a(n) for n = 0..1000</a>
%t A078724 Table[Prime[(n (n + 1)) / 2 + 3], {n, 0, 50}] (* _Vincenzo Librandi_, Jun 08 2016 *)
%o A078724 (PARI) triprimes(n) = { sr = 0; for(j=1,n, x = j*(j+1)/2+2; z = prime(x); sr+=1.0/z; print1(z" "); ); print(); print(sr); }
%o A078724 (Magma) [NthPrime(n*(n+1) div 2+3): n in [0..50]]; // _Vincenzo Librandi_, Jun 08 2016
%Y A078724 Cf. A000040, A078721 (after 7, primes in third diagonal of triangle in comment).
%K A078724 nonn,easy
%O A078724 0,1
%A A078724 _Cino Hilliard_, Dec 20 2002