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A033573
a(n) = (2*n+1)*(9*n+1).
1
1, 30, 95, 196, 333, 506, 715, 960, 1241, 1558, 1911, 2300, 2725, 3186, 3683, 4216, 4785, 5390, 6031, 6708, 7421, 8170, 8955, 9776, 10633, 11526, 12455, 13420, 14421, 15458, 16531, 17640, 18785, 19966, 21183, 22436, 23725, 25050, 26411, 27808, 29241, 30710, 32215, 33756, 35333
OFFSET
0,2
FORMULA
From G. C. Greubel, Oct 12 2019: (Start)
G.f.: (1 + 27*x + 8*x^2)/(1-x)^3.
E.g.f.: (1 + 29*x + 18*x^2)*exp(x). (End)
Sum 1/a(n) = -Psi(1/9)/7 -gamma/7 -2*log(2)/7 = 1.0634904644443440.. where gamma =A001620, Psi(1/9) = -A354636.
MAPLE
seq((2*n+1)*(9*n+1), n=0..50); # G. C. Greubel, Oct 12 2019
MATHEMATICA
Table[(2*n+1)*(9*n+1), {n, 0, 50}] (* G. C. Greubel, Oct 12 2019 *)
PROG
(PARI) a(n)=(2*n+1)*(9*n+1) \\ Charles R Greathouse IV, Jun 17 2017
(Magma) [(2*n+1)*(9*n+1): n in [0..50]] # G. C. Greubel, Oct 12 2019
(Sage) [(2*n+1)*(9*n+1) for n in range(50)] # G. C. Greubel, Oct 12 2019
(GAP) List([0..50], n-> (2*n+1)*(9*n+1)); # G. C. Greubel, Oct 12 2019
CROSSREFS
Sequence in context: A165133 A044217 A044598 * A035076 A308508 A096382
KEYWORD
nonn,easy
STATUS
approved