a(n) = 4*Product_{i=1..n-1} (3^i+1)^2.A119600a(n) = 4*Product_{i=1..n-1} (3^i+1)^2.Terms a(0) =4a(1) =4a(2) =64a(3) =6400a(4) =5017600a(5) =33738342400External referencesoeis: A119600