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A274873

Number of set partitions of [n] into exactly nine blocks such that all odd elements are in blocks with an odd index and all even elements are in blocks with an even index.

1, 4, 70, 280, 2919, 11676, 94944, 379776, 2669361, 10677444, 68321994, 273287976, 1640345707, 6561382828, 37643205652, 150572822608, 836008721925, 3344034887700, 18122573826942, 72490295307768, 385781480224959, 1543125920899836, 8099850233307144

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OFFSET

9,2

LINKS

Alois P. Heinz, Table of n, a(n) for n = 9..1000

FORMULA

G.f.: x^9/((x-1)*(3*x-1)*(2*x+1)*(2*x-1)*(3*x+1)*(4*x-1)*(x+1)* (12*x^2-1)*(6*x^2-1)*(20*x^2-1)*(2*x^2-1)).

EXAMPLE

a(9) = 1: 1|2|3|4|5|6|7|8|9.

a(10) = 4: 1|2(10)|3|4|5|6|7|8|9, 1|2|3|4(10)|5|6|7|8|9, 1|2|3|4|5|6(10)|7|8|9, 1|2|3|4|5|6|7|8(10)|9.

CROSSREFS

Column k=9 of A274537.