OFFSET
0,3
COMMENTS
Also the number of non-isomorphic pairs of set partitions of {1,...,n}.
LINKS
Andrew Howroyd, Table of n, a(n) for n = 0..50
FORMULA
EXAMPLE
Inequivalent representatives of the a(3) = 7 nonnegative integer matrices:
[3] [1 2] [1 1 1] [1 0] [0 1] [1 0 0] [1 0 0]
[0 2] [1 1] [0 1 1] [0 1 0]
[0 0 1]
Non-isomorphic representatives of the a(3) = 7 pairs of set partitions:
{{1,2,3}} {{1,2,3}}
{{1,2,3}} {{1},{2,3}}
{{1,2,3}} {{1},{2},{3}}
{{1},{2,3}} {{1},{2,3}}
{{1},{2,3}} {{2},{1,3}}
{{1},{2,3}} {{1},{2},{3}}
{{1},{2},{3}} {{1},{2},{3}}
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Aug 25 2018
EXTENSIONS
a(6)-a(25) from Andrew Howroyd, Sep 03 2018
Terms a(26) and beyond from Andrew Howroyd, Mar 29 2020
STATUS
approved