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 A065716 Number of 5's in decimal expansion of 2^n. 11

%I

%S 0,0,0,0,0,0,0,0,1,1,0,0,0,0,0,0,2,0,0,1,1,1,0,0,0,2,0,0,2,1,0,0,0,2,

%T 0,1,0,1,0,3,1,4,1,0,1,1,0,2,1,2,1,2,2,1,1,0,2,4,1,2,2,2,0,2,2,0,0,3,

%U 5,5,1,0,1,1,3,2,4,3,3,2,1,3,3,2,1,3,4,4,3,1,1,3,4,1,3,2,4,5,5,2,2

%N Number of 5's in decimal expansion of 2^n.

%C 2^8 = 256 so a(8)=1.

%H Harry J. Smith, <a href="/A065716/b065716.txt">Table of n, a(n) for n = 0..1000</a>

%t Table[ Count[ IntegerDigits[2^n], 5], {n, 0, 100} ]

%o (PARI) Count(x, d)= { local(c=0, f); while (x>9, f=x-10*(x\10); if (f==d, c++); x\=10); if (x==d, c++); return(c) } { for (n=0, 1000, a=Count(2^n, 5); write("b065716.txt", n, " ", a) ) } \\ _Harry J. Smith_, Oct 27 2009

%o (PARI) a(n) = #select(x->(x==5), digits(2^n)); \\ _Michel Marcus_, Jun 15 2018

%Y Cf. 0's A027870, 1's A065712, 2's A065710, 3's A065714, 4's A065715, 6's A065717, 7's A065718, 8's A065719, 9's A065744.

%K nonn,base

%O 0,17

%A _Benoit Cloitre_, Dec 04 2001

%E More terms from _Robert G. Wilson v_, Dec 07 2001

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Last modified May 24 01:29 EDT 2019. Contains 323528 sequences. (Running on oeis4.)