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Number of set partitions of [2n] into exactly n parts such that no part contains two elements with a circular distance less than three.
2

%I #9 Aug 21 2015 09:51:15

%S 1,0,0,1,7,458,18944,858023,42615547,2331292564,140077132527,

%T 9199520194445,656844469384222,50720708063406821,4215138323234299756,

%U 375319710150454887887,35660986210126871452435,3602425696957042245685448,385625195068544676072425069

%N Number of set partitions of [2n] into exactly n parts such that no part contains two elements with a circular distance less than three.

%C The circular distance of 1 and n is 1 (for n>1).

%H Alois P. Heinz, <a href="/A261479/b261479.txt">Table of n, a(n) for n = 0..50</a>

%F a(n) = A261477(2n,n).

%e a(0) = 1: {}.

%e a(3) = 1: 14|25|36.

%e a(4) = 7: 14|26|37|58, 14|27|36|58, 15|26|37|48, 15|26|38|47, 15|27|36|48, 16|25|37|48, 16|25|38|47.

%e a(5) = 458: 147|258|3,10|6|9, 147|258|36|9|10, 147|258|39|6|10, ..., 1|29|36,10|47|58, 1|29|36|47,10|58, 1|2|369|47,10|58.

%Y Cf. A261477.

%K nonn

%O 0,5

%A _Alois P. Heinz_, Aug 20 2015