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A129292
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Number of divisors of n^4 - 1 that are not greater than n.
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5
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1, 1, 2, 2, 4, 2, 6, 4, 5, 3, 8, 3, 10, 4, 6, 4, 12, 4, 13, 4, 11, 6, 14, 3, 10, 6, 12, 6, 17, 3, 16, 7, 10, 9, 13, 4, 18, 7, 11, 4, 22, 3, 26, 8, 9, 7, 23, 5, 18, 7, 13, 6, 25, 4, 24, 8, 21, 6, 18, 3, 18, 10, 12, 14, 16, 4, 26, 8, 17, 7, 31, 5, 30, 6, 11, 13, 26, 7, 25, 6, 16, 10, 35, 4, 18, 11
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OFFSET
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1,3
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COMMENTS
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a(n) = #{d: d<=n and A123865(n) mod d = 0};
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LINKS
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EXAMPLE
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a(100) = #{1,3,9,11,33,73,99} = 7.
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MAPLE
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f:= n -> nops(select(`<=`, numtheory:-divisors(n^4-1), n)):
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MATHEMATICA
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Table[Count[Divisors[n^4-1], _?(#<=n&)], {n, 90}] (* Harvey P. Dale, Aug 13 2014 *)
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PROG
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(PARI) a(n) = if (n==1, 1, sumdiv(n^4-1, d, d <= n)); \\ Michel Marcus, Sep 21 2014
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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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