4987228domain: NAppears in sequencesNumber of integer n-tuples {x(1),x(2),...,x(n)} with the following properties: (1) x(1)=1 and, for k>1, if d=x(k)-x(k-1), then (2) d is relatively prime to x(k-1) and (3) d=x(i) for some i in {1,2,...,k-1}.at n=12A054769