A173399 Partial sums of A000798.

1, 2, 6, 35, 390, 7332, 216859, 9752100, 652531454, 63912820877, 9040966693920, 1825887005430112, 521181458071204133, 208402575114740157174, 115825454552169007964634, 88852094573138413500449755, 93499965506283177978710943850, 134231450058844163850300579669696, 261626767193693218968916427480786899

Offset: 0

Author

Jonathan Vos Post, Feb 17 2010

Keywords

• nonn

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.

Crossrefs

Cf. A000798, A001035 (labeled posets), A001930 (unlabeled topologies), A000112 (unlabeled posets), A006057.

Programs

Mathematica

Cases[Import["https://oeis.org/A000798/b000798.txt", "Table"], {, }][[All, 2]] // Accumulate (* Jean-François Alcover, Dec 30 2019 *)

Formula

a(n) = Sum_{i=0..n} A000798(i).

Extensions

Missing term 7332 added and extended by Jean-François Alcover, Dec 30 2019