a(n) is the number of hierarchical linear models on n unlabeled factors allowing 2-way interactions (but no higher order interactions); or the number of unlabeled simple graphs with <= n nodes.
A006897
a(n) is the number of hierarchical linear models on n unlabeled factors allowing 2-way interactions (but no higher order interactions); or the number of unlabeled simple graphs with <= n nodes.
Terms
- a(0) =1a(1) =2a(2) =4a(3) =8a(4) =19a(5) =53a(6) =209a(7) =1253a(8) =13599a(9) =288267a(10) =12293435a(11) =1031291299a(12) =166122463891
External references
- oeis: A006897