123129

Appears in sequences

• a(0)=1; for n >= 1, a(n) = Sum_{k=0..n} 8^k*N(n,k) where N(n,k) = (1/n)*C(n,k)*C(n,k+1) are the Narayana numbers (A001263).at n=6A082147
• a(n) = N(6,n), where N(6,x) is the 6th Narayana polynomial.at n=8A090199
• Number of strings of length n over a 9-letter alphabet that begin with a nontrivial palindrome.at n=6A249642
• Expansion of (1/x) * Series_Reversion( x / ((1+x)^4 * (x+(1+x)^2)) ).at n=5A387452