login
A236967
Expansion of (1+3*x)^2/(1-3*x)^2.
1
1, 12, 72, 324, 1296, 4860, 17496, 61236, 209952, 708588, 2361960, 7794468, 25509168, 82904796, 267846264, 860934420, 2754990144, 8781531084, 27894275208, 88331871492, 278942752080, 878669669052, 2761533245592, 8661172452084, 27113235502176, 84728860944300
OFFSET
0,2
FORMULA
For n >= 1, a(n) = 4*n*3^n. - Robert Israel, May 08 2014
PROG
(Magma) m:=30; R<x>:=PowerSeriesRing(Integers(), m); Coefficients(R!((1+3*x)^2/(1-3*x)^2));
CROSSREFS
Cf. Expansion of (1 + k*x)^m/(1 - k*x)^m where the values of k,m are:
......|..m = 1..|..m = 2..|..m = 3..|..m = 4..|..m = 5..|..m = 6..|
k = 2 | A151821 | A241204 | | | | |
k = 3 | A099856 | A236967 | | | | |
k = 4 | A081654 | | | | | |
-------------------------------------------------------------------
Sequence in context: A052181 A118979 A014970 * A227022 A036392 A035472
KEYWORD
nonn,easy
AUTHOR
EXTENSIONS
Edited by Wolfdieter Lang, May 07 2014
STATUS
approved