a(n) = (1/4) A374656(n).A374657a(n) = (1/4) A374656(n).Terms a(0) =1a(1) =3a(2) =15a(3) =90a(4) =810a(5) =10530a(6) =210600a(7) =6528600a(8) =319901400a(9) =24952309200External referencesoeis: A374657