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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. 2

%I

%S 1,4,70,280,2919,11676,94944,379776,2669361,10677444,68321994,

%T 273287976,1640345707,6561382828,37643205652,150572822608,

%U 836008721925,3344034887700,18122573826942,72490295307768,385781480224959,1543125920899836,8099850233307144

%N 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.

%H Alois P. Heinz, <a href="/A274873/b274873.txt">Table of n, a(n) for n = 9..1000</a>

%F 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)).

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

%e 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.

%Y Column k=9 of A274537.

%K nonn,easy

%O 9,2

%A _Alois P. Heinz_, Jul 09 2016

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Last modified January 26 07:04 EST 2022. Contains 350572 sequences. (Running on oeis4.)