A026649 a(n) = T(2n,n), T given by A026648.
1, 3, 8, 36, 114, 558, 1856, 9384, 31942, 164322, 566928, 2948184, 10262004, 53761068, 188306112, 991821456, 3490234182, 18458523378, 65190481904, 345875613144, 1225052975644, 6516499594212, 23134851823872, 123325174525104
Offset: 0