Number of collections of subsets of {1, 2, ..., n} that are closed under union and intersection.
A306445
Number of collections of subsets of {1, 2, ..., n} that are closed under union and intersection.
Terms
- a(0) =2a(1) =4a(2) =13a(3) =74a(4) =732a(5) =12085a(6) =319988a(7) =13170652a(8) =822378267a(9) =76359798228
External references
- oeis: A306445