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A121509 5*n^2/2 -5*n +13/4 -(-1)^n/4. 0
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; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..48.

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).

a(n) = 1 + 2(n-1)^2 + floor((n-1)^2/2). [Wesley Ivan Hurt, Jun 14 2013]

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}]

CROSSREFS

Cf. A003215, A005448, A001849.

Sequence in context: A142463 A289575 A086497 * A096071 A230117 A159791

Adjacent sequences:  A121506 A121507 A121508 * A121510 A121511 A121512

KEYWORD

nonn,easy

AUTHOR

Roger L. Bagula, Sep 07 2006

EXTENSIONS

Definition replaced by polynomial - The Assoc. Editors of the OEIS, Oct 14 2009

STATUS

approved

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Last modified June 20 00:47 EDT 2019. Contains 324223 sequences. (Running on oeis4.)