a(n) = (5*7^n+1)/3.

Terms

a(0) =2a(1) =12a(2) =82a(3) =572a(4) =4002a(5) =28012a(6) =196082a(7) =1372572a(8) =9608002a(9) =67256012a(10) =470792082a(11) =3295544572a(12) =23068812002a(13) =161481684012