Number of 2-element intersecting families (with not necessarily distinct sets) of an n-element set.

A053154

Number of 2-element intersecting families (with not necessarily distinct sets) of an n-element set.

Terms

    a(0) =0a(1) =1a(2) =5a(3) =22a(4) =95a(5) =406a(6) =1715a(7) =7162a(8) =29615a(9) =121486a(10) =495275a(11) =2009602a(12) =8124935a(13) =32761366a(14) =131834435a(15) =529712842a(16) =2125993055a(17) =8525430046a(18) =34166159195a(19) =136858084882a(20) =548012945975

External references