Eigensequence of A053121.

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =4a(5) =9a(6) =22a(7) =56a(8) =152a(9) =428a(10) =1257a(11) =3827a(12) =12023a(13) =38975a(14) =129801a(15) =443833a(16) =1554849a(17) =5572334a(18) =20409121a(19) =76283610a(20) =290737945a(21) =1128730320a(22) =4460079331a(23) =17924115817a(24) =73207479057a(25) =303691230784