978792domain: NAppears in sequencesNumber of distinct non-extendable sequences X={x(1),x(2),...,x(k)} where x(1)=1, the x(i)'s are distinct elements of {1,...,n} with |x(i)-x(i+1)|=1 or 2, for i=1,2,...,k.at n=22A054668G.f. satisfies: a(n) = [x^n] ( A(x)^(n+1) + 1/A(x)^(n+1) ) / (n+1) for n>1, with a(0)=a(1)=1.at n=7A243426