a(n) = (1/2)*(1 + 3*i)^n + (1/2)*(1 - 3*i)^n where i = sqrt(-1).

Terms

a(0) =1a(1) =-8a(2) =-26a(3) =28a(4) =316a(5) =352a(6) =-2456a(7) =-8432a(8) =7696a(9) =99712a(10) =122464a(11) =-752192a(12) =-2729024a(13) =2063872a(14) =31417984a(15) =42197248a(16) =-229785344a(17) =-881543168a(18) =534767104a(19) =9884965888a(20) =14422260736a(21) =-70005137408a(22) =-284232882176a(23) =131585609728