a(n) = A371764(n, 2).

Terms

a(0) =1a(1) =14a(2) =86a(3) =374a(4) =1382a(5) =4694a(6) =15206a(7) =47894a(8) =148262a(9) =453974a(10) =1380326a(11) =4177814a(12) =12607142a(13) =37968854a(14) =114201446a(15) =343194134a(16) =1030762022a(17) =3094645334a(18) =9288654566a(19) =27875400854a(20) =83645076902a(21) =250972979414a(22) =752994435686