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A025702 Index of 4^n within sequence of numbers of form 4^i*5^j. 2

%I

%S 1,2,4,7,11,16,22,29,36,44,53,63,74,86,99,112,126,141,157,174,192,211,

%T 230,250,271,293,316,340,365,390,416,443,471,500,530,561,593,625,658,

%U 692,727,763,800,838,876,915,955,996,1038,1081,1125,1169,1214,1260,1307,1355

%N Index of 4^n within sequence of numbers of form 4^i*5^j.

%H Charles R Greathouse IV, <a href="/A025702/b025702.txt">Table of n, a(n) for n = 0..10000</a>

%o (PARI) a(n)=my(N=1); n+1+sum(i=1, n, logint(N<<=2, 5)); \\ _Charles R Greathouse IV_, Jan 11 2018

%o (PARI) first(n)=my(s, N=1/4); vector(n+1, i, s+=logint(N<<=2, 5)+1) \\ _Charles R Greathouse IV_, Jan 11 2018

%Y Differs from A025717 at a(65).

%K nonn,easy

%O 0,2

%A _David W. Wilson_

%E Offset corrected by _Charles R Greathouse IV_, Jan 11 2018

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Last modified October 28 11:38 EDT 2021. Contains 348329 sequences. (Running on oeis4.)