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A065715
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Number of 4's in decimal expansion of 2^n.
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13
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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
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OFFSET
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0,19
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COMMENTS
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2^10 = 1024 so a(10)=1.
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LINKS
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MATHEMATICA
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Table[ Count[ IntegerDigits[2^n], 4], {n, 0, 100} ]
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PROG
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(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)
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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