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A272501
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Number of n-letter strings over a ten letter alphabet where no letter appears exactly three times.
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3
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1, 10, 100, 990, 9640, 91900, 855100, 7754050, 68545360, 592095160, 5020469200, 42054532750, 350538754600, 2926602465940, 24587635740040, 208406304739450, 1784567064858400, 15453880256710000, 135459380264937760, 1202295227210127910, 10804306958861721400
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OFFSET
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0,2
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COMMENTS
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species is SEQ_10(SET_(!=3)(Z))
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LINKS
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FORMULA
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E.g.f.: (exp(z)-z^3/3!)^10.
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EXAMPLE
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a(3) = 10^3-10 because all 3-letter strings qualify except the strings containing only one type of letter.
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MAPLE
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a := n->n!*coeftayl((exp(z)-z^3/3!)^10, z=0, n);
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MATHEMATICA
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With[{nn=20}, CoefficientList[Series[(Exp[x]-x^3/3!)^10, {x, 0, nn}], x] Range[ 0, nn]!] (* Harvey P. Dale, Apr 08 2019 *)
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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STATUS
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approved
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