a(n) = 6^floor((n+1)/2).

Terms

a(0) =1a(1) =6a(2) =6a(3) =36a(4) =36a(5) =216a(6) =216a(7) =1296a(8) =1296a(9) =7776a(10) =7776a(11) =46656a(12) =46656a(13) =279936a(14) =279936a(15) =1679616a(16) =1679616a(17) =10077696a(18) =10077696a(19) =60466176a(20) =60466176a(21) =362797056a(22) =362797056a(23) =2176782336a(24) =2176782336a(25) =13060694016a(26) =13060694016a(27) =78364164096