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A050988
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6-idempotent numbers.
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9
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1, 42, 1008, 18144, 272160, 3592512, 43110144, 480370176, 5043886848, 50438868480, 484213137408, 4489976365056, 40409787285504, 354362750042112, 3037395000360960, 25514118003032064, 210491473525014528, 1708695490967764992, 13669563927742119936, 107917609955858841600
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OFFSET
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6,2
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COMMENTS
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Number of n-permutations of 7 objects: s, t, u, v, z, x, y with repetition allowed, containing exactly six u's. - Zerinvary Lajos, Jun 16 2008
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LINKS
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FORMULA
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a(n) = binomial(n,6)*6^(n-6).
Sum_{n>=6} 1/a(n) = 102561/5 - 112500*log(6/5).
Sum_{n>=6} (-1)^n/a(n) = 605052*log(7/6) - 466341/5. (End)
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MAPLE
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MATHEMATICA
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a[n_] := Binomial[n, 6]*6^(n - 6); Array[a, 20, 6] (* Amiram Eldar, Apr 17 2022 *)
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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