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 A307881 #18 May 06 2019 14:38:23 %S A307881 2,4,11,23,64,68,73,119,143,172,263,452,557,868,1238,1579,2864,3533, %T A307881 3637,4252,5171,9263,11282,12388,20036,59119,69332,90131,113783, %U A307881 139283,178612,185714,413788,468059,579932,960707,1879582,2727031,3266951,3319868,3591593 %N A307881 2*a(n) is the least number where k sets a new record such that 2*a(n)-k and 2*a(n)+k are prime and at least one of 2*a(n)-j and 2*a(n)+j is composite for all 0<j<k. %C A307881 The corresponding records of k are given in A307882. %H A307881 Hugo Pfoertner, <a href="/A307881/b307881.txt">Table of n, a(n) for n = 1..53</a> %o A307881 (PARI) kmax=0; for(n=2,10^7,forstep(k=1,n,2,if(isprime(2*n-k)&&isprime(2*n+k),if(k>kmax,print1(n,", ");kmax=k);break(1)))) %Y A307881 Cf. A065978, A293858, A307882, A325142. %K A307881 nonn %O A307881 1,1 %A A307881 _Hugo Pfoertner_, May 03 2019