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 A134533 #8 Apr 17 2013 16:21:17
%S A134533 1,2,4,8,10,12,18,19,22,24,25,32,33,35,45,56,57,58,59,60,72,73,76,81,
%T A134533 82,84,88,100,102,103,104,105,117,118,125,136,138,142,147,149,162,188,
%U A134533 190,192,195,201,203,206,210,212,232,240,246,252,262,264,265,269,270,280
%N A134533 Numbers n such that the sum of the digits of 7^n is prime.
%H A134533 Vincenzo Librandi, <a href="/A134533/b134533.txt">Table of n, a(n) for n = 1..1000</a>
%e A134533 7^2=49 and 4+9=13 is prime.
%p A134533 P:=proc(n) local cont,i,k,w; if isprime(n) then cont:=0; while cont<1000 do cont:=cont+1; w:=0; k:=n^cont; while k>0 do w:=w+k-(trunc(k/10)*10); k:=trunc(k/10); od; if isprime(w) then print(cont); fi; od; fi; end: P(7);
%t A134533 a={}; For[n=1, n<700, n++, If[PrimeQ[Plus@@IntegerDigits[7^n]], AppendTo[a, n]]];a (* _Vincenzo Librandi_, Apr 17 2013 *)
%Y A134533 Cf. A076203, A134532, A134534, A134535.
%K A134533 easy,nonn,base
%O A134533 1,2
%A A134533 _Paolo P. Lava_ and _Giorgio Balzarotti_, Oct 30 2007