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A336270
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a(n) = Sum_{k=0..n} Sum_{j=0..k} (binomial(n,k) * binomial(k,j))^n.
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4
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1, 3, 15, 381, 67635, 83118753, 813824623689, 58040410068847251, 32150480245981639533315, 154935057570894645075940703673, 5474671509704049919709361235659936825, 1600436120524545216094358662984789029130593831
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OFFSET
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0,2
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LINKS
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FORMULA
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a(n) = (n!)^n * [x^n] (Sum_{k>=0} x^k / (k!)^n)^3.
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MATHEMATICA
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Table[Sum[Sum[(Binomial[n, k] Binomial[k, j])^n, {j, 0, k}], {k, 0, n}], {n, 0, 11}]
Table[(n!)^n SeriesCoefficient[Sum[x^k/(k!)^n, {k, 0, n}]^3, {x, 0, n}], {n, 0, 11}]
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PROG
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(PARI) a(n) = sum(k=0, n, sum(j=0, k, (binomial(n, k) * binomial(k, j))^n)); \\ Michel Marcus, Jul 16 2020
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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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