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

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.

Sequence in context: A308294 A278553 A101841 * A281654 A222309 A061609

Adjacent sequences: A274870 A274871 A274872 * A274874 A274875 A274876

Keyword

nonn,easy

Author

Alois P. Heinz, Jul 09 2016

Status

approved