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A130637
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a(n) = n*a(n-2) + a(n-5) for n >= 5 and with a(0)=0, a(1)=1, a(2)=0, a(3)=3, a(4)=0.
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0
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0, 1, 0, 3, 0, 15, 1, 105, 11, 945, 125, 10396, 1605, 135159, 23415, 2027510, 385036, 34469275, 7065807, 654939640, 143343650, 13754117476, 3188029575, 316351767755, 77167649440, 7908937537525, 2020113002916, 213544501542750, 56879515849403, 6192867712389190
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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(n) = n*a(n-2) + a(n-5) for n >= 5. - Jianing Song, Oct 10 2018
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MATHEMATICA
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RecurrenceTable[{a[0] == 0, a[1] == 1, a[2] == 0, a[3] == 3, a[4] == 0, a[n] == n a[n - 2] + a[n - 5]}, a, {n, 0, 30}] (* Bruno Berselli, Oct 11 2018 *)
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PROG
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(PARI) a(n) = if(n<5, (n==1) + 3*(n==3), n*a(n-2) + a(n-5)) \\ Jianing Song, Oct 10 2018
(Magma) I:=[0, 1, 0, 3, 0]; [n le 5 select I[n] else (n-1)*Self(n-2)+Self(n-5): n in [1..30]]; // Vincenzo Librandi, Oct 11 2018
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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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EXTENSIONS
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Edited, new name, and offset corrected by Jianing Song, Oct 10 2018
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STATUS
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approved
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