A065715 Number of 4's in decimal expansion of 2^n.

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, 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, 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

Offset

0,19

Comments

2^10 = 1024 so a(10)=1.

Links

Harry J. Smith, Table of n, a(n) for n = 0..1000

Mathematica

Table[ Count[ IntegerDigits[2^n], 4], {n, 0, 100} ]

Prog

(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, 4); write("b065715.txt", n, " ", a) ) } \\ Harry J. Smith, Oct 27 2009
(PARI) a(n) = #select(x->(x==4), digits(2^n)); \\ Michel Marcus, Jun 15 2018
(Python)
def A065715(n):
    return str(2**n).count('4') # Chai Wah Wu, Feb 14 2020

Crossrefs

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.

Sequence in context: A238857 A253587 A110962 * A180984 A051628 A163540

Adjacent sequences: A065712 A065713 A065714 * A065716 A065717 A065718

Keyword

nonn,base

Author

Benoit Cloitre, Dec 04 2001

Extensions

More terms from Robert G. Wilson v, Dec 07 2001

Status

approved