Numerator of (2^n - 1)*n! / 2^(n+1).

Terms

a(0) =0a(1) =1a(2) =3a(3) =21a(4) =45a(5) =465a(6) =2835a(7) =40005a(8) =80325a(9) =1448685a(10) =14501025a(11) =319178475a(12) =1915538625a(13) =49810085325a(14) =697383762075