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 A260683 Number of 2's in the expansion of 2^n in base 3. 3
 0, 1, 0, 2, 1, 1, 1, 2, 0, 4, 2, 4, 3, 3, 2, 6, 5, 5, 3, 7, 4, 7, 5, 4, 1, 5, 2, 8, 8, 7, 9, 9, 8, 7, 7, 8, 4, 6, 8, 9, 11, 11, 7, 11, 10, 8, 9, 8, 8, 10, 11, 16, 13, 10, 9, 12, 13, 16, 12, 13, 15, 15, 11, 15, 16, 14, 14, 12, 14, 15, 14, 16, 11, 18, 11, 17, 10 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,4 COMMENTS Erdős conjectures that a(n) > 0 for n > 8. REFERENCES R. K. Guy, Unsolved Problems in Number Theory, B33. [Does not seem to be in section B33.] LINKS Robert Israel, Table of n, a(n) for n = 0..10000 FORMULA a(n) = A020915(n) - A104320(n) - A036461(n). - Altug Alkan, Nov 15 2015 a(n) = A081603(A000079(n)). - Michel Marcus, Dec 03 2015 EXAMPLE For n=5, the expansion of 2^n in number base 3 is 1012, thus: a(n)=1 For n=10, the expansion of 2^n in number base 3 is 1101221, thus: a(n)=2 MAPLE seq(numboccur(2, convert(2^n, base, 3)), n=0..100); # Robert Israel, Nov 15 2015 MATHEMATICA S={}; n=-1; While[n<150, n++; A=IntegerDigits[2^n, 3]; k=Count[A, 2]; AppendTo[S, k]]; S PROG (PARI) c(k, d, b) = {my(c=0, f); while (k>b-1, f=k-b*(k\b); if (f==d, c++); k\=b); if (k==d, c++); return(c)} for(n=0, 300, print1(c(2^n, 2, 3)", ")) \\ Altug Alkan, Nov 15 2015 (PARI) a(n) = #select(x->(x==2), digits(2^n, 3)); \\ Michel Marcus, Nov 28 2018 (Perl) use ntheory ":all"; sub a260683 { scalar grep { \$_==2 } todigits(vecprod((2) x shift), 3) } # Dana Jacobsen, Aug 16 2016 CROSSREFS Cf. A004642 (2^n in base 3), A020915 (number of terms), A036461 (number of 1's), A104320 (number of 0's). Cf. A000108 (conjecture that A000108(n) is 6m+1 only for n = 0, 1 and 5 follows from Erdős's one). Sequence in context: A163819 A301734 A281185 * A337683 A092673 A243842 Adjacent sequences:  A260680 A260681 A260682 * A260684 A260685 A260686 KEYWORD base,easy,nonn AUTHOR Emmanuel Vantieghem, Nov 15 2015 STATUS approved

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Last modified January 18 13:13 EST 2021. Contains 340254 sequences. (Running on oeis4.)