a(n) = A026626(2*n-1, n-2).

Terms

a(0) =1a(1) =7a(2) =30a(3) =119a(4) =467a(5) =1820a(6) =7076a(7) =27493a(8) =106848a(9) =415538a(10) =1617504a(11) =6302416a(12) =24581249a(13) =95968478a(14) =375029576a(15) =1466881997a(16) =5742440324a(17) =22498218218a(18) =88212326756a(19) =346114729562