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A216093 a(n) = 10^n - (5^(2^n) mod 10^n). 7
5, 75, 375, 9375, 9375, 109375, 7109375, 87109375, 787109375, 1787109375, 81787109375, 81787109375, 81787109375, 40081787109375, 740081787109375, 3740081787109375, 43740081787109375, 743740081787109375 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

a(n)^3 mod 10^n = a(n).

a(n) is the unique positive integer less than 10^n such that a(n) is divisible by 5^n and a(n) + 1 is divisible by 2^n. - Eric M. Schmidt, Sep 01 2012

a(n+1) + a(n)^2 == 0 (mod 10^(n+1)). - Robert Israel, Apr 24 2017

LINKS

Robert Israel, Table of n, a(n) for n = 1..999

FORMULA

2^(4*5^(n-1)) mod 10^n - 1.

MAPLE

f:= n -> (-5 &^(2^n) mod 10^n):

map(f, [$1..30]); # Robert Israel, Apr 24 2017

PROG

(Sage) def A216093(n) : return crt(-1, 0, 2^n, 5^n) # Eric M. Schmidt, Sep 01 2012

CROSSREFS

Cf. A007185, A016090, A216092, A091663, A018248.

Sequence in context: A285452 A048350 A030991 * A151752 A127212 A091903

Adjacent sequences:  A216090 A216091 A216092 * A216094 A216095 A216096

KEYWORD

nonn

AUTHOR

V. Raman, Sep 01 2012

STATUS

approved

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Last modified July 19 22:14 EDT 2019. Contains 325168 sequences. (Running on oeis4.)