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 A078400 #9 Nov 17 2019 15:54:43
%S A078400 2,3,5,7,2,5,2,5,7,2,5,7,7,2,7,2,5,5,2,5,7,5,2,2,7,2,5,7,5,2,7,2,5,5,
%T A078400 7,2,7,5,7,2,7,5,2,5,5,7,7,2,7,2,2,5,5,7,5,2,2,5,7,5,7,2,5,2,7,2,7,7,
%U A078400 7,5,5,5,2,2,7,2,5,7,2,2,5,2,5,2,7,5,2,5,7,5,7,7,7,2,5,2,7,2,2,5,7,2,5,7,7
%N A078400 Iterated sum-of-digits of A078403(n).
%H A078400 Cino Hilliard, <a href="/A078400/a078400.txt">Proof of the Digital Root Theorem</a>, posted on Yahoo group B2LCC, Feb 17 2003
%o A078400 (PARI) drp(n) = { forprime(x=2,n, r = x%9; if(isprime(r), print1(r" "); ); ); }
%Y A078400 Cf. A038194, A078403.
%K A078400 easy,nonn,base
%O A078400 1,1
%A A078400 _Cino Hilliard_, Dec 24 2002
%E A078400 More terms from _Joshua Zucker_, Jul 24 2006