cp's OEIS Frontend

A320168 Number of ways to group the first 2*n positive integers into n pairs (xi, yi) with xi < yi, and such that the n numbers (yi mod xi) are all different.

%I A320168 #41 Oct 21 2018 04:10:59
%S A320168 1,1,2,2,7,12,22,26,85,226,717,1695,5071,14275,47405,176747,638329,
%T A320168 2166516
%N A320168 Number of ways to group the first 2*n positive integers into n pairs (xi, yi) with xi < yi, and such that the n numbers (yi mod xi) are all different.
%C A320168 How does a(n+1)/a(n) behave as n increases?
%H A320168 David A. Corneth, <a href="/A320168/a320168_2.png">Illustration for a(4)</a>
%e A320168 a(3) = 2 because {(1,3), (2,5), (4,6)} and {(1,5), (2,3), (4,6)} are corresponding sets.
%e A320168 a(4) = 7 because {(1,6), (2,5), (3,8), (4,7)}, {(1,3), (2,7), (4,6), (5,8)}, {(1,7), (2,3), (4,6), (5,8)}, {(1,3), (2,5), (4,7), (6,8)}, {(1,5), (2,3), (4,7), (6,8)}, {(1,2), (3,7), (4,6), (5,8)}, {(1,2), (3,8), (4,7), (5,6)} are corresponding sets.
%Y A320168 Cf. A002968, A060963, A272363, A320129.
%K A320168 nonn,more
%O A320168 0,3
%A A320168 _Altug Alkan_, Oct 07 2018
%E A320168 a(13)-a(17) from _Rémy Sigrist_, Oct 07 2018