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A357533
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a(n) = Sum_{k=0..floor(n/4)} (n-3*k)!/(n-4*k)!.
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5
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1, 1, 1, 1, 2, 3, 4, 5, 8, 13, 20, 29, 46, 77, 128, 205, 338, 581, 1012, 1733, 2990, 5293, 9536, 17117, 30778, 56165, 104108, 193621, 360662, 677693, 1289080, 2467373, 4735826, 9142837, 17814308, 34950245, 68835118, 136197581, 271384112, 544302973, 1096578410, 2218459013, 4513377436
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OFFSET
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0,5
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LINKS
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FORMULA
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a(n) = (3 * a(n-1) + n * a(n-4) + 1)/4 for n > 3.
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PROG
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(PARI) a(n) = sum(k=0, n\4, (n-3*k)!/(n-4*k)!);
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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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