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A092467
a(n) = Sum_{i+j+k=n, 0<=i,j,k<=n} (n+2k)!/(i! * j! * (3*k)!).
3
1, 3, 13, 63, 309, 1511, 7373, 35951, 175269, 854455, 4165565, 20307647, 99002389, 482649479, 2352978861, 11471077391, 55922991237, 272631840855, 1329115610269, 6479611111519, 31588945184245, 154000207833639
OFFSET
0,2
COMMENTS
In general, Sum_{k=0..n} C(n+2k,3k)*r^k has g.f. (1-r*x)^2/(1-(3r+1)*x+3r^2*x^2-r^3*x^3). - Paul Barry, Aug 23 2007
FORMULA
G.f.: (1-4x+4x^2)/(1-7x+12x^2-8x^3). - Ralf Stephan, Dec 02 2004
a(n) = Sum_{k=0..n} C(n+2k,3k)*2^(n-k). - Paul Barry, Aug 23 2007
CROSSREFS
Cf. A007583.
Sequence in context: A350478 A276893 A284160 * A034478 A026715 A001850
KEYWORD
nonn
AUTHOR
Benoit Cloitre, Mar 25 2004
STATUS
approved