a(n) is the number of regular D classes in the semigroup of all binary relations on [n].
A173311
a(n) is the number of regular D classes in the semigroup of all binary relations on [n].
Terms
- a(0) =1a(1) =2a(2) =4a(3) =9a(4) =25a(5) =88a(6) =406a(7) =2451a(8) =19450a(9) =202681a(10) =2769965a(11) =49519392a(12) =1154411138a(13) =34978238590
External references
- oeis: A173311