A048473 prefixed by two zeros.

Terms

a(0) =0a(1) =0a(2) =1a(3) =5a(4) =17a(5) =53a(6) =161a(7) =485a(8) =1457a(9) =4373a(10) =13121a(11) =39365a(12) =118097a(13) =354293a(14) =1062881a(15) =3188645a(16) =9565937a(17) =28697813a(18) =86093441a(19) =258280325a(20) =774840977a(21) =2324522933a(22) =6973568801a(23) =20920706405a(24) =62762119217a(25) =188286357653a(26) =564859072961