Zeroth trisection of A246584.

Terms

a(0) =1a(1) =12a(2) =92a(3) =470a(4) =2020a(5) =7456a(6) =24962a(7) =76736a(8) =221156a(9) =602200a(10) =1565088a(11) =3902344a(12) =9389022a(13) =21876192a(14) =49542464a(15) =109333520a(16) =235717092a(17) =497416856a(18) =1029271544a(19) =2091480776a(20) =4179123296a(21) =8220922592a(22) =15937506968a(23) =30477650240a(24) =57540075230a(25) =107327212780a(26) =197923648864