Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #7 Jan 10 2018 16:18:27
%S 1,4,9,16,25,36,49,64,81,100,121,145,171,199,229,261,295,331,369,409,
%T 451,496,543,592,643,696,751,808,867,928,991,1056,1124,1194,1266,1340,
%U 1416,1494,1574,1656,1740,1826,1915,2006,2099,2194,2291,2390,2491,2594,2699
%N Index of 10^n within sequence of numbers of form 3^i*10^j.
%H Charles R Greathouse IV, <a href="/A025741/b025741.txt">Table of n, a(n) for n = 1..10000</a>
%o (PARI) a(n)=my(N=1); n+sum(i=2,n, logint(N*=10,3)); \\ _Charles R Greathouse IV_, Jan 10 2018
%o (PARI) first(n)=my(s,N=1/10); vector(n,i, s+=logint(N*=10,3)+1) \\ _Charles R Greathouse IV_, Jan 10 2018
%K nonn,easy
%O 1,2
%A _David W. Wilson_