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 A131558 #9 Sep 27 2016 05:31:02
%S A131558 2,24133,870530414842019,11138479445180240497,
%T A131558 1948856725874605823462196012533593
%N A131558 Primes which are the sum of the first 10^k primes for some k.
%C A131558 Also numbers n such that A099824(n) is prime.
%e A131558 The sum of the first 10^1 primes is 129 which is not prime and not in the sequence. The sum of the first 10^9 primes is 11138479445180240497 which is prime and in the sequence.
%o A131558 (PARI)
%o A131558 sm=0; ct=0; p=1; bb=1;
%o A131558 { while ( 1,
%o A131558 p = nextprime(p+1); sm += p; ct++;
%o A131558 if ( (ct==bb), if ( isprime(sm),print1(sm,", ")); bb*=10; );
%o A131558 ); }
%Y A131558 Cf. A099824.
%K A131558 nonn,more
%O A131558 1,1
%A A131558 _Cino Hilliard_, Aug 27 2007
%E A131558 a(5) from _David Baugh_, Sep 27 2016