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A200047
Number of compositions of n having smallest part equal to 2.
2
0, 1, 0, 1, 2, 3, 5, 9, 15, 25, 42, 70, 116, 192, 317, 522, 858, 1408, 2307, 3775, 6170, 10074, 16433, 26784, 43623, 71002, 115497, 187777, 305147, 495669, 804839, 1306404, 2119884, 3438952, 5577396, 9043549, 14660810, 23762784, 38509220, 62397495, 101090631
OFFSET
1,5
LINKS
FORMULA
G.f.: (x-1)^2*x^2/(1-2*x+x^4+x^5).
EXAMPLE
a(7) = 5: [2,2,3], [2,3,2], [2,5], [3,2,2], [5,2].
MAPLE
a:= n-> (<<0|1|0|0|0>, <0|0|1|0|0>, <0|0|0|1|0>, <0|0|0|0|1>, <-1|-1|0|0|2>>^n. <<0, 0, 1, 0, 1>>)[1, 1]: seq (a(n), n=1..50);
CROSSREFS
Column k=2 of A105147.
Sequence in context: A097083 A268709 A326024 * A147877 A003476 A017989
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Nov 13 2011
STATUS
approved