a(n) = 3*a(n-1) + 4*a(n-2), with a(0)=1, a(1)=2.

Terms

a(0) =1a(1) =2a(2) =10a(3) =38a(4) =154a(5) =614a(6) =2458a(7) =9830a(8) =39322a(9) =157286a(10) =629146a(11) =2516582a(12) =10066330a(13) =40265318a(14) =161061274a(15) =644245094a(16) =2576980378a(17) =10307921510a(18) =41231686042a(19) =164926744166a(20) =659706976666