cp's OEIS Frontend

A025694 Index of 2^n within sequence of numbers of form 2^i * 9^j.

%I A025694 #16 Jul 06 2025 13:29:52
%S A025694 1,2,3,4,6,8,10,13,16,19,23,27,31,36,41,46,52,58,64,70,77,84,91,99,
%T A025694 107,115,124,133,142,152,162,172,183,194,205,217,229,241,253,266,279,
%U A025694 292,306,320,334,349,364,379,395,411,427,444,461,478,496,514,532,550,569,588,607
%N A025694 Index of 2^n within sequence of numbers of form 2^i * 9^j.
%C A025694 Positions of zeros in A025678. - _R. J. Mathar_, Jul 06 2025
%H A025694 Robert Israel, <a href="/A025694/b025694.txt">Table of n, a(n) for n = 0..10000</a>
%p A025694 f:= proc(n) local j,s,t;
%p A025694       t:= n;
%p A025694       for j from 1 do
%p A025694          s:= ilog2(9^j);
%p A025694          if s >= n then return t fi;
%p A025694          t:= t + n-1-s;
%p A025694       od
%p A025694 end proc:
%p A025694 map(f, [$1..100]); # _Robert Israel_, Dec 09 2016
%o A025694 (PARI) a(n)=my(N=1); n+1+sum(i=1, n, logint(N<<=1, 9)); \\ _Charles R Greathouse IV_, Jan 11 2018
%o A025694 (PARI) first(n)=my(s, N=1/2); vector(n+1, i, s+=logint(N<<=1, 9)+1) \\ _Charles R Greathouse IV_, Jan 11 2018
%K A025694 nonn,easy
%O A025694 0,2
%A A025694 _David W. Wilson_
%E A025694 Offset corrected by _Charles R Greathouse IV_, Jan 11 2018