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%I #7 Sep 03 2015 19:07:49
%S 0,1,0,0,0,1,1,0,1,1,1,3,1,1,2,2,0,2,1,1,3,1,0,3,0,1,4,1,2,5,1,4,2,7,
%T 1,4,4,4,3,0,3,3,3,3,5,4,1,2,2,6,2,3,5,6,6,5,7,6,6,7,4,7,5,5,6,6,3,8,
%U 1,3,7,6,8,6,7,7,1,5,7,5,4,9,7,6,10,7,7,7,4,14,8,5,10,8,10,13,11,6,7,6,6
%N Number of 7's in decimal expansion of 7^n.
%p P:=proc(n) local i,k,x,y,w,cont; y:=7; k:=y; for i from 0 by 1 to n do x:=y^i; cont:=0; while x>0 do w:=x-trunc(x/10)*10; if w=k then cont:=cont+1; fi; x:=trunc(x/10); od; print(cont); od; end: P(100);
%t DigitCount[7^Range[0,100],10,7] (* _Harvey P. Dale_, Sep 03 2015 *)
%Y Cf. A065710, A126205, A126206, A126207, A126208, A126210, A126211.
%K base,nonn
%O 0,12
%A _Paolo P. Lava_ and _Giorgio Balzarotti_, Dec 20 2006
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