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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 (list; graph; refs; listen; history; text; internal format)
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

Giovanni Resta, Table of n, a(n) for n = 1..10000

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 * A202804 A155192 A229720

Adjacent sequences:  A239831 A239832 A239833 * A239835 A239836 A239837

KEYWORD

nonn,base

AUTHOR

Giovanni Resta, Mar 27 2014

STATUS

approved

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Last modified September 16 02:16 EDT 2019. Contains 327088 sequences. (Running on oeis4.)