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A121509
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5*n^2/2 -5*n +13/4 -(-1)^n/4.
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0
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1, 3, 11, 23, 41, 63, 91, 123, 161, 203, 251, 303, 361, 423, 491, 563, 641, 723, 811, 903, 1001, 1103, 1211, 1323, 1441, 1563, 1691, 1823, 1961, 2103, 2251, 2403, 2561, 2723, 2891, 3063, 3241, 3423, 3611, 3803, 4001, 4203, 4411, 4623, 4841, 5063, 5291, 5523
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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FORMULA
| a(n)= 2*a(n-1) -2*a(n-3) +a(n-4). G.f.: -x*(1+x+5*x^2+3*x^3)/(1+x)/(x-1)^3).
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MATHEMATICA
| M := {{0, 1}, {-1, 2} } v[1] = {1, 7} w[n_] = If[Mod[n, 2] == 0, {0, 4}, {0, 6}] v[n_] := v[n] = M.v[n - 1] + w[n] a = Table[v[n][[1]], {n, 1, 30}]
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CROSSREFS
| Cf. A003215, A005448, A001849.
Sequence in context: A132209 A142463 A086497 * A096071 A159791 A078723
Adjacent sequences: A121506 A121507 A121508 * A121510 A121511 A121512
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KEYWORD
| nonn,easy
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AUTHOR
| Roger Bagula (rlbagulatftn(AT)yahoo.com), Sep 07 2006
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EXTENSIONS
| Definition replaced by polynomial - The Assoc. Editors of the OEIS, Oct 14 2009
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