a(n) = 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) = 3, |s(i) - s(i-1)| <= 1 for i >= 2. Also a(n) = T(n,n-3), where T is the array defined in A026105.
A026109
a(n) = 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) = 3, |s(i) - s(i-1)| <= 1 for i >= 2. Also a(n) = T(n,n-3), where T is the array defined in A026105.
Terms
- a(0) =1a(1) =3a(2) =10a(3) =30a(4) =89a(5) =259a(6) =748a(7) =2148a(8) =6150a(9) =17578a(10) =50204a(11) =143364a(12) =409500a(13) =1170300a(14) =3346944a(15) =9579840a(16) =27444681a(17) =78698475a(18) =225887010a(19) =648985414a(20) =1866356437a(21) =5372348487a(22) =15478733108a(23) =44637360700a(24) =128837626255a(25) =372183158061
External references
- oeis: A026109