Number of universes with n entities, exactly one being the empty set, which satisfy the Axiom of Extensionality (two sets are identical when they have the same elements) and are closed under taking subsets.
A156972
Number of universes with n entities, exactly one being the empty set, which satisfy the Axiom of Extensionality (two sets are identical when they have the same elements) and are closed under taking subsets.
Terms
- a(0) =1a(1) =2a(2) =6a(3) =60a(4) =840a(5) =18720a(6) =559440a(7) =22196160a(8) =1092631680a(9) =65768371200
External references
- oeis: A156972