a(0)=1, a(1)=4; thereafter a(n) = a(n-2)+2*A055099(n-1)+2^(n-1).

Terms

a(0) =1a(1) =4a(2) =11a(3) =36a(4) =119a(5) =408a(6) =1419a(7) =4988a(8) =17631a(9) =62528a(10) =222163a(11) =790180a(12) =2812135a(13) =10011304a(14) =35647259a(15) =126942540a(16) =452078447a(17) =1610033040a(18) =5734081251a(19) =20421960308a(20) =72733344375a(21) =259042555640a(22) =922591559467