It appears that table 2 of the Williamson article contains typographical errors and the sequence was intended to read as in A210699.
Table of n, a(n) for n=2..10.
Williamson, S. G. The combinatorial analysis of patterns and the principle of inclusion-exclusion. Discrete Math. 1 (1972), no. 4, 357--388. MR0299493 (45 #8541)
Cf. A210766, A060560, A295925.
Sequence in context: A167472 A199040 A094592 * A332193 A167058 A167067
Adjacent sequences: A210765 A210766 A210767 * A210769 A210770 A210771
N. J. A. Sloane, Mar 25 2012