a(n) = Sum_{j=n..2n} j!.A374574a(n) = Sum_{j=n..2n} j!.Terms a(0) =1a(1) =3a(2) =32a(3) =870a(4) =46224a(5) =4037880a(6) =522956160a(7) =93928267440External referencesoeis: A374574