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 A196223 #18 Apr 03 2023 10:36:12
%S A196223 6,7,15,27,41,55,172,561,1334,6571,11490,429705,2173016,4417701,
%T A196223 9063353,9531624,40411847,64538709,83537963,121316228,181504240,
%U A196223 222586609
%N A196223 Natural numbers n such that Sum_{k = 1..pi(n)-1} p(k) == p(pi(n)) mod n, where p(k) denotes the k-th prime and pi(n) is the number of primes strictly less than n.
%H A196223 G. L. Honaker, Jr. and Chris Caldwell, <a href="https://t5k.org/curios/cpage/20463.html">Prime Curios! 6571</a>
%e A196223 2+3+5+7+11==13 (mod 15) and so 15 has this property.
%t A196223 Reap[Module[{c = 0}, For[n = 4, n <= 10^6, n++, If[PrimeQ[n - 1], c += NextPrime[n - 1, -1]]; If[Mod[c, n] == NextPrime[n, -1], Sow[n]]]]]
%Y A196223 Cf. A000720.
%K A196223 nonn
%O A196223 1,1
%A A196223 _Jake Foster_, Sep 29 2011