a(n) = number of (s(0),s(1),...,s(n)) such that every s(i) is a nonnegative integer, s(0) = 1, s(n) = 2, |s(1) - s(0)| = 1, |s(i) - s(i-1)| <= 1 for i >= 2. Also a(n) = T(n,n-1), where T is the array in A026120; a(n) = U(n,n+1), where U is the array in A026148.
A026123
a(n) = number of (s(0),s(1),...,s(n)) such that every s(i) is a nonnegative integer, s(0) = 1, s(n) = 2, |s(1) - s(0)| = 1, |s(i) - s(i-1)| <= 1 for i >= 2. Also a(n) = T(n,n-1), where T is the array in A026120; a(n) = U(n,n+1), where U is the array in A026148.
Terms
- a(0) =1a(1) =4a(2) =10a(3) =28a(4) =76a(5) =209a(6) =575a(7) =1589a(8) =4405a(9) =12253a(10) =34189a(11) =95679a(12) =268503a(13) =755457a(14) =2130717a(15) =6023235a(16) =17063139a(17) =48434514a(18) =137741280a(19) =392407134a(20) =1119766942a(21) =3200326627a(22) =9160055809a(23) =26254474379a(24) =75348899051a(25) =216515177336a(26) =622887159274
External references
- oeis: A026123