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A140065
a(n) = (7*n^2 - 17*n + 12)/2.
1
1, 3, 12, 28, 51, 81, 118, 162, 213, 271, 336, 408, 487, 573, 666, 766, 873, 987, 1108, 1236, 1371, 1513, 1662, 1818, 1981, 2151, 2328, 2512, 2703, 2901, 3106, 3318, 3537, 3763, 3996, 4236, 4483, 4737, 4998, 5266, 5541, 5823, 6112, 6408, 6711, 7021, 7338, 7662
OFFSET
1,2
COMMENTS
Binomial transform of [1, 2, 7, 0, 0, 0, ...].
This sequence and 1, 6, 18, 37, 63, 96, ... with signature (3,-3,1) [not yet in OEIS] together contain all numbers k, so that 56*k - 47 is a square. - Klaus Purath, Oct 21 2021
FORMULA
A007318 * [1, 2, 7, 0, 0, 0, ...].
a(n) = A000217(n) + 6*A000217(n-2) = (A140064(n) + A140066(n))/2. - R. J. Mathar, May 06 2008
O.g.f.: x*(1+6*x^2)/(1-x)^3. - Alexander R. Povolotsky, May 06 2008
a(n) = 7*n + a(n-1) - 12 for n > 1, a(1)=1. - Vincenzo Librandi, Jul 08 2010
a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3), n >= 4. - Klaus Purath, Oct 21 2021
E.g.f.: exp(x)*(6 - 5*x + 7*x^2/2) - 6. - Elmo R. Oliveira, Oct 31 2024
EXAMPLE
a(4) = 28 = (1, 3, 3, 1) * (1, 2, 7, 0) = (1 + 6 + 21 + 0).
MAPLE
seq((12-17*n+7*n^2)*1/2, n=1..40); # Emeric Deutsch, May 07 2008
MATHEMATICA
Table[(7 n^2 - 17 n + 12)/2, {n, 1, 50}] (* Bruno Berselli, Mar 12 2015 *)
LinearRecurrence[{3, -3, 1}, {1, 3, 12}, 50] (* Harvey P. Dale, May 28 2017 *)
PROG
(PARI) x = 'x + O('x^50); Vec(x*(1+6*x^2)/(1-x)^3) \\ G. C. Greubel, Feb 23 2017
(Magma) [(7*n^2 - 17*n + 12)/2 : n in [1..60]]; // Wesley Ivan Hurt, Oct 10 2021
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Gary W. Adamson, May 03 2008
EXTENSIONS
More terms from R. J. Mathar and Emeric Deutsch, May 06 2008
More terms from Vladimir Joseph Stephan Orlovsky, Oct 25 2008
STATUS
approved