OFFSET
0,2
COMMENTS
Number of different quasi-orders (or topologies, or transitive digraphs) with n labeled elements.
The subsequence of primes in this partial sum begins: 2, 216859.
FORMULA
a(n) = Sum_{i=0..n} A000798(i).
MATHEMATICA
Cases[Import["https://oeis.org/A000798/b000798.txt", "Table"], {_, _}][[All, 2]] // Accumulate (* Jean-François Alcover, Dec 30 2019 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Jonathan Vos Post, Feb 17 2010
EXTENSIONS
Missing term 7332 added and extended by Jean-François Alcover, Dec 30 2019
STATUS
approved