A239834 a(n) is the smallest k such that the first n powers of k have an even number of digits in base 10.

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

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 * A337148 A202804 A155192

Adjacent sequences: A239831 A239832 A239833 * A239835 A239836 A239837

Keyword

nonn,base

Author

Giovanni Resta, Mar 27 2014

Status

approved