2,8

The Bruck-Ryser theorem says that a(n)=0 if n == 1 or 2 (mod 4) and is not the sum of two squares.

CRC Handbook of Combinatorial Designs, 1996, p. 695.

Handbook of Combinatorics, North-Holland '95, p. 672.

C. W. H. Lam, The Search for a Finite Projective Plane of Order 10, American Mathematical Monthly, 98, (no. 4) 1991, 305 - 318.

C. W. H. Lam, G. Kolesova and S. Swiercz, A computer search for finite projective planes of order 9, Discrete Math., 92 (1991), 187-195.

C. W. H. Lam, L. Thiel and S. Swiercz, The non-existence of finite projective planes of order 10, Canad. J. Math., 41 (1989), 1117-1123.

C. W. H. Lam, Publications

Ed Pegg, Jr., Finite affines planes of low orders

N. J. A. Sloane, My favorite integer sequences, in Sequences and their Applications (Proceedings of SETA '98).

Eric Weisstein's World of Mathematics, Projective Planes

Sequence in context: A058473 A115527 A050920 this_sequence A141150 A089418 A124856

Adjacent sequences: A001228 A001229 A001230 this_sequence A001232 A001233 A001234

nonn,hard,nice

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