It was shown by Abrham that the number of pure Skolem sequences of order n, n 0 or 1 (mod 4), and the number of extended Skolem sequences of order n, are both bounded below by 2 n/3 . These results are extended to give similar lower bounds for the numbers of hooked Skolem sequences, split Skolem sequences and split-hooked Skolem sequences.
G. K. Bennett, Mike J. Grannell, Terry S. Griggs