OFFSET
0,2
COMMENTS
Partial sums of A014915. - Bruno Berselli, Oct 26 2012
Convolution of A003462(n+1) with itself. - Philippe Deléham, Mar 07 2014
LINKS
Bruno Berselli, Table of n, a(n) for n = 0..1000
Jean-Luc Baril, Pamela E. Harris, and José L. Ramírez, Flattened Catalan Words, arXiv:2405.05357 [math.CO], 2024. See p. 16.
S. Kitaev, J. Remmel, and M. Tiefenbruck, Marked mesh patterns in 132-avoiding permutations I, arXiv:1201.6243v1 [math.CO], 2012. See (16).
Sergey Kitaev, Jeffrey Remmel, and Mark Tiefenbruck, Quadrant Marked Mesh Patterns in 132-Avoiding Permutations II, Electronic Journal of Combinatorial Number Theory, Volume 15 #A16. (arXiv:1302.2274)
Index entries for linear recurrences with constant coefficients, signature (8,-22,24,-9).
FORMULA
From Bruno Berselli, May 11 2012: (Start)
G.f.: 1/((1-x)^2*(1-3*x)^2).
a(n) = 1+n*(1+9*3^n)/4. (End)
E.g.f.: exp(x)*(4 + x + 27*exp(2*x)*x)/4. - Stefano Spezia, May 14 2024
EXAMPLE
a(0) = 1*1 = 1;
a(1) = 1*4 + 4*1 = 8;
a(2) = 1*13 + 4*4 + 13*1 = 42;
a(3) = 1*40 + 4*13 + 13*4 + 40*1 = 184;
a(4) = 1*121 + 4*40 + 13*13 + 40*4 + 121*1 = 731; etc. - Philippe Deléham, Mar 07 2014
MATHEMATICA
Table[1 + n ((1 + 9 3^n)/4), {n, 0, 25}] (* Bruno Berselli, May 11 2012 *)
CoefficientList[Series[1/(1-4x+3x^2)^2, {x, 0, 30}], x] (* or *) LinearRecurrence[ {8, -22, 24, -9}, {1, 8, 42, 184}, 30] (* Harvey P. Dale, Jun 14 2020 *)
PROG
(Magma) m:=26; R<x>:=PowerSeriesRing(Integers(), m); Coefficients(R!(1/((1-x)^2*(1-3*x)^2))); // Bruno Berselli, May 11 2012
(PARI) Vec(1/(1-4*x+3*x^2)^2 + O(x^100)) \\ Altug Alkan, Nov 01 2015
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, May 09 2012
STATUS
approved