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a(n) is the number of digits in the decimal representation of the smallest power of 6 that contains n consecutive identical digits.
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%I #8 Nov 23 2013 13:52:18

%S 1,4,4,90,176,289,1170,6640,21569,21569,54421

%N a(n) is the number of digits in the decimal representation of the smallest power of 6 that contains n consecutive identical digits.

%C Number of digits in 6^k is equal to floor(1 + k*log_10(6)).

%t k = 0; Join[{1}, Table[While[d = IntegerDigits[6^k]; prt = Partition[Differences[d], n - 1, 1]; ! MemberQ[prt, Table[0, {n - 1}]], k++]; Length[d], {n, 2, 8}]] (* _T. D. Noe_, Oct 03 2012 *)

%Y Cf. A215729, A215735.

%K nonn,base

%O 1,2

%A _V. Raman_, Sep 27 2012

%E a(11) added by _V. Raman_, Nov 23 2013