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 A049847 #9 Mar 06 2020 23:14:12
%S A049847 1,1,1,2,1,1,2,1,1,2,1,2,3,1,1,2,3,1,2,1,1,2,1,2,3,1,2,3,1,1,2,3,1,2,
%T A049847 1,1,2,3,1,2,1,2,3,1,2,3,4,1,2,1,1,2,1,1,2,1,2,3,4,5,6,7,1,2,1,2,3,1,
%U A049847 1,2,3,4,5,1,1,2,3,1,2,3,1,2,1,2,3,1,2,3,1,1,2,3,4
%N A049847 a(n) = (2*n + 1 - prevprime(2*n+1))/2.
%t A049847 Table[(2n+1-NextPrime[2n+1,-1])/2,{n,2,100}] (* _Harvey P. Dale_, Jul 25 2015 *)
%Y A049847 Cf. A049613, A049653, A049711, A049716.
%K A049847 nonn
%O A049847 2,4
%A A049847 _N. J. A. Sloane_