0,2

The Y function of order n is a self-dual monotone Boolean function of (n+1)(n+2)/2 points arranged in a triangular grid, with n+1 points on each side. Suppose we place black or white stones on that grid.

Then, as apparently first pointed out by John Milnor about 1950, either the white or black stones form a "Y" - that is, they touch all three sides of the board. (The corner points each touch two of the sides.)

The Y function tells us whether the white stones or the black stones have the Y.

D. E. Knuth, The Art of Computer Programming, Vol. 4A, Exercise 7.1.1-67.

Cf. A134953.

Adjacent sequences: A134949 A134950 A134951 this_sequence A134953 A134954 A134955

Sequence in context: A033505 A063782 A071718 this_sequence A149028 A126183 A042039

nonn

D. E. Knuth, Jan 26 2008