21074012

Appears in sequences

• Sum C(n-3k,3k+1), k=0..floor(n/6).at n=37A102516
• a(n) = Sum_{k=0..floor(n/3)} binomial(n+3*k,n-3*k).at n=19A373905
• Expansion of (1 + x)/(1 - x^3*(1 + x)^3).at n=37A375319