1,2

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

N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).

M. A. Sainte-Lagu\"{e}, Les R\'{e}seaux (ou Graphes)}, M\'{e}morial des Sciences Math\'{e}matiques, Fasc. 18, Gauthier-Villars, Paris, 1926, p. 49.

a(5) = 16 because it is impossible to attack all squares with 2 queens but with 3 queens you can do it in 16 different ways (with mirroring and rotation).

Sequence in context: A075499 A099394 A059991 this_sequence A111661 A072651 A093035

Adjacent sequences: A002565 A002566 A002567 this_sequence A002569 A002570 A002571

nonn

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

a(9)-a(12) from Johan Sarnbratt (johan.sarnbratt(AT)gmail.com), Mar 28 2008