18457764317domain: NAppears in sequencesNumber of (s(0), s(1), ..., s(n)) such that s(0) = 0, |s(i) - s(i-1)| = 1 for i = 1,2,3; |s(i) - s(i-1)| <= 1 for i >= 4, s(n) = 3; also a(n) = T(n,n-3), where T is the array defined in A026082.at n=21A026086