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A265376
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a(1) = 1 and a(n) = Sum_{i=1..n-1} (-1)^i*i*a(i).
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2
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1, -1, -3, 6, 30, -120, -840, 5040, 45360, -362880, -3991680, 39916800, 518918400, -6227020800, -93405312000, 1307674368000, 22230464256000, -355687428096000, -6758061133824000, 121645100408832000, 2554547108585472000, -51090942171709440000, -1175091669949317120000
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OFFSET
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1,3
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COMMENTS
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1/abs(a(n)) + 1/abs(a(n+1)) = 1/(n-1)!, n = 3,5,7,... hence Sum_{n>1} 1/abs(a(n)) = cosh(1). - Peter McNair, Mar 04 2022
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LINKS
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FORMULA
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MATHEMATICA
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a[1]=1; a[n_] := a[n] = Sum[(-1)^i*i*a[i], {i, 1, n - 1}]; Array[a, 33]
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CROSSREFS
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KEYWORD
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sign
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AUTHOR
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STATUS
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approved
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