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A216092
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a(n) = 2^(2*5^(n-1)) mod 10^n.
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5
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4, 24, 624, 624, 90624, 890624, 2890624, 12890624, 212890624, 8212890624, 18212890624, 918212890624, 9918212890624, 59918212890624, 259918212890624, 6259918212890624, 56259918212890624, 256259918212890624
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OFFSET
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1,1
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COMMENTS
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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 2^n and a(n) + 1 is divisible by 5^n. - Eric M. Schmidt, Sep 01 2012
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LINKS
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FORMULA
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a(n) = 5^(2^n) mod 10^n - 1.
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MATHEMATICA
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Table[PowerMod[5, 2^n, 10^n], {n, 20}]-1 (* Harvey P. Dale, Dec 17 2017 *)
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PROG
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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