Half the number of permutations of 0..n with exactly two maxima.

Terms

a(0) =0a(1) =0a(2) =1a(3) =8a(4) =44a(5) =208a(6) =912a(7) =3840a(8) =15808a(9) =64256a(10) =259328a(11) =1042432a(12) =4180992a(13) =16748544a(14) =67047424a(15) =268304384a(16) =1073463296a(17) =4294377472a(18) =17178624000a(19) =68716855296a(20) =274872401920