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a(n) = the highest power of 5 with n decimal digits.
1

%I #5 Dec 10 2016 18:49:38

%S 5,25,625,3125,78125,390625,9765625,48828125,244140625,6103515625,

%T 30517578125,762939453125,3814697265625,95367431640625,

%U 476837158203125,2384185791015625,59604644775390625,298023223876953125

%N a(n) = the highest power of 5 with n decimal digits.

%C a(n) = 5^d(n), with

%C d(n) = {1, 2, 4, 5, 7, 8, 10, 11, 12, 14, 15, 17, 18, 20, 21, 22, 24, 25, 27, 28}.

%C If we redefine the sequence as a(n) = the highest power of 5 less than 10^n, then keyword "base" may be omitted.

%C d(n) = A066344(n). - _Zak Seidov_, Oct 01 2010

%t d[n_]=Floor@Log[5, 10^n]; a[n_]=5^d[n]

%K base,nonn

%O 1,1

%A _Zak Seidov_, Sep 29 2010