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

LINKS

Table of n, a(n) for n=1..21.

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: A244586 A114546 A067471 * A014553 A227422 A121855

Adjacent sequences:  A102688 A102689 A102690 * A102692 A102693 A102694

KEYWORD

fini,full,nonn,base,changed

AUTHOR

Lekraj Beedassy, Jan 21 2005

EXTENSIONS

Edited by Charles R Greathouse IV, Aug 03 2010

STATUS

approved

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Last modified July 27 02:39 EDT 2017. Contains 289840 sequences.