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A060073
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a(n) = (n^(n-1)-1)/(n-1)^2.
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12
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1, 2, 7, 39, 311, 3268, 42799, 672605, 12345679, 259374246, 6140565047, 161792257795, 4696537119847, 148943500129544, 5124095576030431, 190082780764323705, 7563707819165039903, 321380710796022350410, 14523213296398891966759, 695546073617378871592991
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OFFSET
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2,2
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COMMENTS
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Written in base n, a(n) has n-2 digits and looks like 12345... except that the final digit is n-1 rather than n-2.
Note that 2^m-1 divides a(m+1) = ((m+1)^m-1)/m^2 if and only if m = 2^k-1 with gcd(k,m) = 1. Mersenne numbers M = 2^p-1 such that a(M+1)/(2^M-1) is prime are Mersenne primes 2^3-1 = 7 and 2^7-1 = 127. - Thomas Ordowski, Sep 19 2021
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LINKS
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FORMULA
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EXAMPLE
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a(10) = 999999999/81 = 111111111/9 = 12345679.
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MATHEMATICA
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PROG
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(PARI) { for (n=2, 200, write("b060073.txt", n, " ", (n^(n - 1) - 1)/(n - 1)^2); ) } \\ Harry J. Smith, Jul 01 2009
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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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