a(n) = (4*n+2)! * Sum_{k=0..n} 1 / (4*k+2)!.A337729a(n) = (4*n+2)! * Sum_{k=0..n} 1 / (4*k+2)!.Terms a(0) =1a(1) =361a(2) =1819441a(3) =43710250585External referencesoeis: A337729