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A239834
a(n) is the smallest k such that the first n powers of k have an even number of digits in base 10.
1
10, 32, 47, 57, 64, 69, 72, 75, 78, 80, 82, 83, 84, 85, 86, 87, 88, 88, 89, 90, 90, 91, 91, 91, 92, 92, 92, 93, 93, 93, 93, 94, 94, 94, 94, 94, 94, 95, 95, 95, 95, 95, 95, 95, 96, 96, 96, 96, 96, 96, 96, 96, 96, 96, 96, 96, 97, 97, 97, 97, 97, 97, 97, 97, 97
OFFSET
1,1
COMMENTS
The smallest term with 4 digits is a(230) = 9901 and the smallest with 6 digits is a(23025) = 999901.
LINKS
EXAMPLE
a(3) = 47 because 47 is the smallest n such that n, n^2 and n^3 (here 47, 2209 and 103823) have an even number of digits.
MATHEMATICA
a[n_] := a[n] = Block[{k = If[n == 1, 10, a[n-1]]}, While[! And @@ EvenQ[ IntegerLength[ k^Range[n]]], k++]; k]; Array[a, 100]
CROSSREFS
Sequence in context: A136335 A008422 A063926 * A337148 A202804 A155192
KEYWORD
nonn,base
AUTHOR
Giovanni Resta, Mar 27 2014
STATUS
approved