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A220699
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a(0)=0, a(1)=0; for n>1, a(n) = a(n-1) + (n-4)*a(n-2) + 1
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2
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0, 0, 1, 2, 3, 6, 13, 32, 85, 246, 757, 2480, 8537, 30858, 116229, 455668, 1850417, 7774102, 33679941, 150291472, 689170529, 3244125554, 15649195077, 77287580604, 390271482145, 2013310674830, 10599283282021
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OFFSET
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0,4
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LINKS
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FORMULA
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a(0)=a(1)=0, a(2)=1, a(n) = 2*a(n-1)+(n-5)*a(n-2)-(n-5)*a(n-3).
a(n) ~ (sqrt(Pi)/2+sqrt(2)) * n^(n/2-3/2)*exp(sqrt(n)-n/2-1/4) * (1-29/(24*sqrt(n))). - Vaclav Kotesovec, Dec 27 2012
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MATHEMATICA
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RecurrenceTable[{a[1]==0, a[2]==0, a[n]==a[n-1] + (n-5) a[n-2] + 1}, a, {n, 40}]
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PROG
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(Magma) [n le 2 select 0 else Self(n-1)+(n-5)*Self(n-2) + 1: n in [1..30]];
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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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