
LINKS

Table of n, a(n) for n=13..18.
A. Betten, More information
Ed Pegg, Jr., An example of a 27_4 configuration [In barycentric coordinates, both lines and points are triples. A point is on a line if point.line = 0. The following set of 27 points and 27 lines is a 27_4 configuration, since every point is on 4 lines and every line passes through 4 points: {{2, 3, 1}, {2, 4, 1}, {1, 2, 4}, {1, 0, 2}, {1, 1, 1}, {1, 1,2}, {1, 2, 3}, {1, 2, 4}, {0, 2, 1}, {0, 2, 1}, {1, 2, 3}, {1, 1, 1}, {1, 0, 2}, {1, 1, 1}, {1, 1, 2}, {1, 2, 1}, {1, 2,1}, {2, 1, 0}, {2, 1, 1}, {2, 1, 0}, {2, 1, 1}, {2, 3, 1}, {2, 4, 1}, {3, 1, 2}, {3, 1, 2}, {4, 1, 2}, {4, 1, 2}}.]
