A173488 Partial sums of A055512.

1, 2, 4, 10, 46, 426, 6816, 164778, 5561666, 248740730, 14187451940, 1002045820690, 85615117761142, 8682866612715706, 1029036311254555560, 140656568448867136650, 21929110364021381812410, 3862525357012048643891882, 762298016068721625860646524

Offset: 0

Author

Jonathan Vos Post, Feb 19 2010

Keywords

• nonn
• hard
• more

Comments

Partial sums of the number of lattices with n labeled elements. After a(0) = 1, always even, hence the only prime in the partial sum is 2. The subsequence of semiprimes begins 4, 10, 46.

Crossrefs

Cf. A055512, A006966, A001035, Main diagonal of A058159.

Programs

Mathematica

Cases[Import["https://oeis.org/A055512/b055512.txt", "Table"], {, }][[All, 2]] // Accumulate (* Jean-François Alcover, Jan 02 2020 *)

Formula

a(n) = Sum_{i=0..n} A055512(i).

Extensions

a(17)-a(18) from Jean-François Alcover, Jan 02 2020