Bisection of A001523.

Terms

a(0) =1a(1) =4a(2) =15a(3) =47a(4) =130a(5) =330a(6) =784a(7) =1765a(8) =3804a(9) =7898a(10) =15880a(11) =31048a(12) =59220a(13) =110484a(14) =202070a(15) =362974a(16) =641368a(17) =1116325a(18) =1916184a(19) =3247088a(20) =5436972a(21) =9002752a(22) =14752316a(23) =23938188a(24) =38487496a(25) =61344055a(26) =96974176a(27) =152110204a(28) =236837795a(29) =366177506