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A102691
Least n-expodigital number (i.e., numbers m such that m^n has exactly n decimal digits).
1
0, 4, 5, 6, 7, 7, 8, 8, 8, 8, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9
OFFSET
1,2
COMMENTS
10^(n-1) being the smallest n-digit number, n-expodigital numbers exist iff 10^(n-1) < 9^n, i.e., iff n-1 < n*log_10(9); this condition holds for all n up to 21 because beyond we have, for instance, 20 < 22*log_10(9) < 21. Thus numbers can be at most 21-expodigital.
FORMULA
a(n) = 10 - A102690(n).
EXAMPLE
a(3)=5 because this is the first number followed by 6,7,8 and 9 which are all 3-expodigital: 5^3 = 125; 6^3 = 216; 7^3 = 343; 8^3 = 512; 9^3 = 729.
CROSSREFS
Cf. A102690.
Essentially the same as A067471. - R. J. Mathar, Aug 30 2008
Sequence in context: A334501 A114546 A067471 * A014553 A227422 A121855
KEYWORD
fini,full,nonn,base
AUTHOR
Lekraj Beedassy, Jan 21 2005
EXTENSIONS
Edited by Charles R Greathouse IV, Aug 03 2010
STATUS
approved