a(n) = n! * [x^n] 2*(tan(x))^2*(sec(x) + tan(x)).

Terms

a(0) =0a(1) =0a(2) =4a(3) =12a(4) =56a(5) =240a(6) =1324a(7) =7392a(8) =49136a(9) =337920a(10) =2652244a(11) =21660672a(12) =196658216a(13) =1859020800a(14) =19192151164a(15) =206057828352