a(n) = A026637(2*n-1, n-2).

Terms

a(0) =1a(1) =7a(2) =28a(3) =112a(4) =439a(5) =1711a(6) =6652a(7) =25846a(8) =100450a(9) =390670a(10) =1520764a(11) =5925718a(12) =23112931a(13) =90239407a(14) =352654084a(15) =1379410438a(16) =5400188206a(17) =21157958962a(18) =82959736504a(19) =325514137048