The number of distinct principal ideals in the semigroup of binary relations on an n-set.
A007903
The number of distinct principal ideals in the semigroup of binary relations on an n-set.
Terms
- a(0) =2a(1) =4a(2) =11a(3) =60a(4) =877a(5) =42944a(6) =7339704
External references
- oeis: A007903