1,2

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

R. W. Robinson, Counting labeled acyclic digraphs, pp. 239-273 of F. Harary, editor, New Directions in the Theory of Graphs. Academic Press, NY, 1973.

V. Jovovic and G. Kilibarda, Enumeration of labeled initially-finally connected digraphs, Scientific review, Serbian Scientific Society, 19-20 (1996) 237-247.

V. Jovovic and G. Kilibarda, Enumeration of labeled quasi-initially connected digraphs, Discrete Math., 224 (2000), 151-163.

Sequence in context: A075869 A126685 A105639 this_sequence A069343 A084882 A091502

Adjacent sequences: A003025 A003026 A003027 this_sequence A003029 A003030 A003031

nonn,easy,nice

N. J. A. Sloane (njas(AT)research.att.com).

Corrected and extended by Vladeta Jovovic, Goran Kilibarda (vladeta(AT)eunet.rs)