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A122581
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a(n) = a(n - 1) - 2*a(n - 2) + a(n - 3) - 4*a(n - 4) + 2*a(n - 5).
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5
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1, 1, 1, 1, 1, -2, -5, -2, 4, 13, 19, -5, -50, -65, -20, 118, 283, 187, -311, -914, -1001, 334, 3040, 4405, 835, -8273, -17030, -11189, 20068, 60178, 60427, -29165, -192491, -274310, -39845, 553798, 1070812, 635629, -1341437, -3836765, -3693914, 2237287, 12425356, 16921054, 1409755, -36343973
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OFFSET
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1,6
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COMMENTS
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This recursion is inspired by Ulam's early experiments in derivative recursions.
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LINKS
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FORMULA
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G.f.: x*(1+2*x^2+x^3+5*x^4)/(1-x+2*x^2-x^3+4*x^4-2*x^5). - R. J. Mathar, Nov 18 2007
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MAPLE
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MATHEMATICA
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a[n_]:= a[n]= If[n<6, 1, a[n-1] -2*a[n-2] +a[n-3] -2*(2*a[n-4] -a[n-5])];
Table[a[n], {n, 50}]
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PROG
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(Sage)
def a(n): return 1 if (n<6) else a(n-1) -2*a(n-2) +a(n-3) -4*a(n-4) +2*a(n-5)
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CROSSREFS
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KEYWORD
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sign
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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