a(n) = 2*A000984(n) - 1.

Terms

a(0) =1a(1) =3a(2) =11a(3) =39a(4) =139a(5) =503a(6) =1847a(7) =6863a(8) =25739a(9) =97239a(10) =369511a(11) =1410863a(12) =5408311a(13) =20801199a(14) =80233199a(15) =310235039a(16) =1202160779a(17) =4667212439a(18) =18150270599a(19) =70690527599a(20) =275693057639