0,2

This can be interpreted as the number of ways to choose 2n+1 cells in a hexagonal grid of side n+1 such that no two are in the same row or left diagonal or right diagonal. - Alex Fink (a00(AT)shaw.ca), Mar 16 2005

B. T. Bennett and R. B. Potts, Arrays and brooks, J. Austral. Math. Soc., 7 (1967), 23-31.

A. Kotzig and P. J. Laufer, When are permutations additive?, Amer. Math. Monthly, 85 (1978), 364-365.

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

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

C. Bebeacua, T. Mansour, A. Postnikov and S. Severini, On the x-rays of permutations

a(2) = 6 corresponds to

..O.X.X.......X.X.O.......O.X.X.......X.O.X.......X.O.X.......X.X.O

.X.X.O.X.....X.O.X.X.....X.X.X.O.....X.X.X.O.....O.X.X.X.....O.X.X.X

X.X.X.X.O...O.X.X.X.X...X.O.X.X.X...O.X.X.X.X...X.X.X.X.O...X.X.X.O.X

.O.X.X.X.....X.X.X.O.....X.X.X.O.....X.O.X.X.....X.X.O.X.....O.X.X.X

..X.O.X.......X.O.X.......O.X.X.......X.X.O.......O.X.X.......X.X.O

Sequence in context: A006117 A118025 A119966 this_sequence A126340 A136639 A027109

Adjacent sequences: A002044 A002045 A002046 this_sequence A002048 A002049 A002050

nonn,nice

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

More terms from Alex Fink (a00(AT)shaw.ca), Mar 16 2005