a(n) = number of (s(0),s(1),...,s(n)) such that every s(i) is a nonnegative integer, s(0) = 1, s(n) = 4, |s(1) - s(0)| = 1, |s(i) - s(i-1)| <= 1 for i >= 2. Also a(n) = T(n,n-3), where T is the array in A026120.

A026125

a(n) = number of (s(0),s(1),...,s(n)) such that every s(i) is a nonnegative integer, s(0) = 1, s(n) = 4, |s(1) - s(0)| = 1, |s(i) - s(i-1)| <= 1 for i >= 2. Also a(n) = T(n,n-3), where T is the array in A026120.

Terms

    a(0) =1a(1) =3a(2) =11a(3) =35a(4) =110a(5) =336a(6) =1013a(7) =3021a(8) =8945a(9) =26345a(10) =77297a(11) =226161a(12) =660387a(13) =1925535a(14) =5608710a(15) =16325814a(16) =47500227a(17) =138168589a(18) =401865485a(19) =1168854085a(20) =3400065944a(21) =9892187162a(22) =28787163584a(23) =83796367200a(24) =243997380575a(25) =710704813221

External references