A065719 - OEIS

%I #25 Aug 02 2024 11:32:58

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

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

%U 2,2,1,4,2,0,7,3,1,4,0,4,2,2,5,1,4,3,1,1,4,1,3,6,1,1,7,3,1,5,1,4,1

%N Number of 8's in decimal expansion of 2^n.

%C 2^7 = 128 so a(7)=1.

%H Harry J. Smith, <a href="/A065719/b065719.txt">Table of n, a(n) for n = 0..1000</a>

%t Table[ Count[ IntegerDigits[2^n], 8], {n, 0, 100} ]

%t DigitCount[2^Range[0,100],10,8] (* _Harvey P. Dale_, Aug 02 2024 *)

%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) }

%o { for (n=0, 1000, a=Count(2^n, 8); write("b065719.txt", n, " ", a) ) } \\ _Harry J. Smith_, Oct 27 2009

%o (PARI) a(n) = #select(x->(x==8), digits(2^n)); \\ _Michel Marcus_, Jun 15 2018

%o (Python)

%o def A065719(n):

%o     return str(2**n).count('8') # _Chai Wah Wu_, Feb 14 2020

%Y Cf. 0's A027870, 1's A065712, 2's A065710, 3's A065714, 4's A065715, 5's A065716, 6's A065717, 7's A065718, 9's A065744.

%K nonn,base

%O 0,20

%A _Benoit Cloitre_, Dec 04 2001

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