A126206 - OEIS

%I #13 May 19 2019 17:47:56

%S 0,1,0,1,0,1,1,1,0,2,1,3,0,1,2,2,2,1,1,3,0,3,3,3,2,2,2,3,1,2,2,3,4,3,

%T 1,3,3,4,2,4,2,4,2,2,3,4,3,3,3,3,2,2,3,5,2,4,2,4,4,3,3,3,4,4,6,5,5,4,

%U 2,9,5,2,4,6,4,7,4,2,5,4,3,4,8,4,7,9,2,8,4,7,3,10,9,5,3,5,8,8,3,10,4

%N Number of 4's in the decimal expansion of 4^n.

%H Robert Israel, <a href="/A126206/b126206.txt">Table of n, a(n) for n = 0..10000</a>

%e a(11)=3 because 4^11 = 4194304 with three 4's.

%p P:=proc(n) local i,k,x,y,w,cont; y:=4; 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);

%p # Alternative:

%p map(n -> numboccur(4, convert(4^n,base,10)), [$0..100]); # _Robert Israel_, Jul 18 2018

%t DigitCount[4^#,10,4]&/@Range[0,150]  (* _Harvey P. Dale_, Feb 01 2011 *)

%Y Cf. A065710, A126205, A126207, A126208, A126209, A126210, A126211.

%K nonn,base

%O 0,10

%A _Paolo P. Lava_ and _Giorgio Balzarotti_, Dec 20 2006