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%I #10 Apr 17 2013 16:52:26
%S 1,9,10,11,13,15,19,21,22,25,31,32,51,52,57,58,59,62,63,68,69,70,75,
%T 76,80,81,84,91,93,95,98,99,100,101,103,107,109,114,117,124,131,132,
%U 133,135,137,139,142,153,158,159,161,164,175,176,182,190,192,194,198,207
%N Numbers n such that the sum of the digits of 11^n is prime.
%H Vincenzo Librandi, <a href="/A134534/b134534.txt">Table of n, a(n) for n = 1..1000</a>
%e 11^9=2357947691 and 2+3+5+7+9+4+7+6+9+1=53 is prime.
%p 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(11);
%t Select[Range[250],PrimeQ[Total[IntegerDigits[11^#]]]&] (* _Harvey P. Dale_, Sep 29 2012 *)
%Y Cf. A076203, A134532, A134533, A134535.
%K easy,nonn,base
%O 1,2
%A _Paolo P. Lava_ and _Giorgio Balzarotti_, Oct 30 2007