a(n) = floor((3^n - 2^n)/n).

Terms

a(0) =1a(1) =2a(2) =6a(3) =16a(4) =42a(5) =110a(6) =294a(7) =788a(8) =2130a(9) =5802a(10) =15918a(11) =43945a(12) =122010a(13) =340470a(14) =954409a(15) =2686324a(16) =7588770a(17) =21508796a(18) =61144062a(19) =174286791a(20) =498012192a(21) =1426221150a(22) =4092816966a(23) =11767198302a(24) =33890202200a(25) =97761489210a(26) =282424565454a(27) =817018714982