681528

Appears in sequences

• Triangular numbers n such that psi(n) is also a triangular number, where psi is the Dedekind psi function (A001615).at n=5A292063
• a(n) = Sum_{k=0..floor(n/4)} (-1)^k * binomial(n-1-3*k,k) * binomial(2*n-8*k,n-4*k).at n=11A360295