28545857

Appears in sequences

• Let phi = arccos(1/3), the dihedral angle of the regular tetrahedron. Then cos(n*phi) = a(n)/3^n.at n=16A025172
• Expansion of (1 - x)/(1 - 2*x + 3*x^2) in powers of x.at n=32A087455
• a(n) = Sum_{k=0..n} (-n)^k * binomial(2*n,2*k).at n=8A333991