On an asymptotic formula for the Niven numbers. Cooper, Curtis N.; Kennedy, Robert E. — 1985 International Journal of Mathematics and Mathematical Sciences
A generalization of a theorem by Cheo and Yien concerning digital sums. Cooper, Curtis N.; Kennedy, Robert E. — 1986 International Journal of Mathematics and Mathematical Sciences
Tau numbers, natural density, and Hardy and Wright's theorem 437. Kennedy, Robert E.; Cooper, Curtis N. — 1990 International Journal of Mathematics and Mathematical Sciences
On the natural density of the range of the terminating nines function. Kennedy, Robert K.; Cooper, Curtis N.; Drobot, Vladimir; Hickling, Fred — 1989 International Journal of Mathematics and Mathematical Sciences