a(n) = (4*n+3)! * Sum_{k=0..n} 1 / (4*k+3)!.A337730a(n) = (4*n+3)! * Sum_{k=0..n} 1 / (4*k+3)!.Terms a(0) =1a(1) =841a(2) =6660721a(3) =218205219961External referencesoeis: A337730