A276031 Number of edges in the graded poset of the partitions of n taken modulo 3, where a partition into k parts is joined to a partition into k+1 parts if the latter is a refinement of the former.

0, 1, 2, 5, 9, 14, 21, 30, 41, 54, 70, 89, 110, 135, 164, 195, 231, 272, 315, 364, 419, 476, 540, 611, 684, 765, 854, 945, 1045, 1154, 1265, 1386, 1517, 1650, 1794, 1949, 2106, 2275, 2456, 2639, 2835, 3044, 3255, 3480, 3719, 3960, 4216, 4487, 4760, 5049, 5354

Offset

1,3

Links

Alois P. Heinz, Table of n, a(n) for n = 1..10000

Index entries for linear recurrences with constant coefficients, signature (2,-1,2,-4,2,-1,2,-1).

Formula

G.f.: (x^6-2*x^5+x^4-x^3+2*x^2+1)*x^2/((x^2+x+1)^2*(x-1)^4). - Alois P. Heinz, Aug 27 2016

Example

a(6) = 14, the 14 edges are:  (111111) - (21111), (21111) - (1110), (21111) - (2211), (1110) - (111), (1110) - (210), (2211) - (111), (2211) - (210), (2211) - (222), (210) - (00), (210) - (21), (111) - (21), (222) - (21), (00) - (0), (21) - (0).

Crossrefs

Cf. A000097, A140144.

Sequence in context: A139423 A363459 A026053 * A011905 A306674 A098065

Adjacent sequences: A276028 A276029 A276030 * A276032 A276033 A276034

Keyword

nonn,easy

Author

Caleb Ji, Aug 17 2016

Extensions

More terms from Alois P. Heinz, Aug 27 2016

Status

approved