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A122972
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a(1) = 1, a(2) = 2; for n>2, a(n+1) = a(n)*(n-1) + a(n-1)*n.
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2
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1, 2, 4, 14, 58, 302, 1858, 13262, 107698, 980942, 9905458, 109844942, 1327159858, 17353902542, 244180971058, 3678842132942, 59089527531058, 1007972756756942, 18199148360427058, 346736152866068942
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OFFSET
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1,2
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COMMENTS
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a(n+2) - a(n) = 3*(n-1)*(n-1)! = A052673(n).
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LINKS
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FORMULA
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a(n) = 2*(-1)^n - 3*(-1)^n*Sum_{k=0..n-1} (-1)^k*k!. - Vaclav Kotesovec, Oct 28 2012
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MATHEMATICA
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RecurrenceTable[{a[1]==1, a[2]==2, a[n]==a[n-1](n-2)+a[n-2](n-1)}, a, {n, 20}] (* Harvey P. Dale, Nov 02 2011 *)
Table[2*(-1)^n-3*(-1)^n*Sum[(-1)^k*k!, {k, 0, n-1}], {n, 1, 20}] (* Vaclav Kotesovec, Oct 28 2012 *)
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PROG
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(Haskell)
a122972 n = a122972_list !! (n-1)
a122972_list = 1 : 2 : zipWith (+)
(zipWith (*) [2..] a122972_list) (zipWith (*) [1..] $ tail a122972_list)
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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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