a(n) = A054145(n)/2.

Terms

a(0) =0a(1) =1a(2) =6a(3) =29a(4) =128a(5) =536a(6) =2168a(7) =8556a(8) =33152a(9) =126640a(10) =478304a(11) =1789840a(12) =6646272a(13) =24519680a(14) =89956224a(15) =328437184a(16) =1194102784a(17) =4325299456a(18) =15615510016a(19) =56209986816a(20) =201798074368a(21) =722731821056