login
A275906
Expansion of (1+x+x^2) / (1-4*x-4*x^2-x^3).
1
1, 5, 25, 121, 589, 2865, 13937, 67797, 329801, 1604329, 7804317, 37964385, 184679137, 898378405, 4370194553, 21258970969, 103415040493, 503066240401, 2447184094545, 11904416380277, 57909468139689, 281702722174409, 1370353177636669, 6666133067384001, 32427647702257089, 157745476256201029
OFFSET
0,2
LINKS
T. Doslic, T. Short, Maximal matchings in polyspiro and benzenoid chains, arXiv:1511.00590, [math.CO], 2015. See Th. 3.4.
FORMULA
a(n) = 4*a(n-1)+4*a(n-2)+a(n-3). - Colin Barker, Aug 26 2016
PROG
(PARI) Vec((1+x+x^2)/(1-4*x-4*x^2-x^3) + O(x^40)) \\ Colin Barker, Aug 26 2016
CROSSREFS
Sequence in context: A343801 A218989 A078717 * A249454 A250347 A278282
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Aug 25 2016
STATUS
approved