4,2

W. M. B. Dukes, On the number of matroids on a finite set

Bell(n+1) - (n^2+n+4)2^(n-2) + n(n+1)(3n^2-n+10)/24.

Sequence in context: A123568 A111675 A142495 this_sequence A156150 A125419 A138440

Adjacent sequences: A100725 A100726 A100727 this_sequence A100729 A100730 A100731

nonn

Ralf Stephan, Nov 29 2004