This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A065715 #26 Dec 05 2024 18:55:58
%S A065715 0,0,1,0,0,0,1,0,0,0,1,1,1,0,1,0,0,0,2,1,1,0,3,0,0,2,1,1,2,0,2,3,2,1,
%T A065715 1,1,1,2,3,1,0,0,3,0,3,1,3,2,2,2,2,1,2,2,3,0,1,2,2,3,2,1,3,1,4,3,3,2,
%U A065715 1,0,3,4,3,4,4,0,2,2,4,3,2,3,4,3,2,0,2,4,3,3,4,5,3,2,3,1,3,1,3,3,2
%N A065715 Number of 4's in decimal expansion of 2^n.
%C A065715 2^10 = 1024 so a(10)=1.
%H A065715 Harry J. Smith, <a href="/A065715/b065715.txt">Table of n, a(n) for n = 0..1000</a>
%t A065715 Table[ Count[ IntegerDigits[2^n], 4], {n, 0, 100} ]
%o A065715 (PARI) a(n) = #select(x->(x==4), digits(2^n)); \\ _Michel Marcus_, Jun 15 2018
%o A065715 (Python)
%o A065715 def A065715(n):
%o A065715 return str(2**n).count('4') # _Chai Wah Wu_, Feb 14 2020
%Y A065715 Cf. 0's A027870, 1's A065712, 2's A065710, 3's A065714, 5's A065716, 6's A065717, 7's A065718, 8's A065719, 9's A065744.
%K A065715 nonn,base
%O A065715 0,19
%A A065715 _Benoit Cloitre_, Dec 04 2001
%E A065715 More terms from _Robert G. Wilson v_, Dec 07 2001