Number of (s(0), s(1), ..., s(n)) such that every s(i) is a nonnegative integer, s(0) = 0, s(1) = 1 = s(n), |s(i) - s(i-1)| <= 1 for i >= 2, |s(2) - s(1)| = 1, |s(3) - s(2)| = 1 if s(2) = 1. Also T(n,n-1), where T is the array in A026268.

A026270

Number of (s(0), s(1), ..., s(n)) such that every s(i) is a nonnegative integer, s(0) = 0, s(1) = 1 = s(n), |s(i) - s(i-1)| <= 1 for i >= 2, |s(2) - s(1)| = 1, |s(3) - s(2)| = 1 if s(2) = 1. Also T(n,n-1), where T is the array in A026268.

Terms

    a(0) =1a(1) =2a(2) =6a(3) =15a(4) =39a(5) =102a(6) =270a(7) =721a(8) =1941a(9) =5262a(10) =14354a(11) =39372a(12) =108528a(13) =300482a(14) =835278a(15) =2330334a(16) =6522882a(17) =18313542a(18) =51559506a(19) =145530291a(20) =411738723a(21) =1167450066a(22) =3316925794a(23) =9441771081a(24) =26923831029a(25) =76901809810a(26) =219992462862a(27) =630245628681

External references