Number of final Tic-Tac-Toe positions on a (2*n) X 3 board that resulted in a tie.

Terms

a(0) =1a(1) =18a(2) =28a(3) =58a(4) =140a(5) =334a(6) =824a(7) =2038a(8) =5084a(9) =12730a(10) =32004a(11) =80694a(12) =204004a(13) =516902a(14) =1312336a(15) =3337682a(16) =8502132a(17) =21688182a(18) =55395140a(19) =141651742a(20) =362601356a(21) =929084578a(22) =2382677360a(23) =6115461118a(24) =15707982020a(25) =40375223374a(26) =103846409504a(27) =267258086338a(28) =688201711116