a(n) = 6*a(n-2) for n > 2; a(1) = 4, a(2) = 1.

Terms

a(0) =4a(1) =1a(2) =24a(3) =6a(4) =144a(5) =36a(6) =864a(7) =216a(8) =5184a(9) =1296a(10) =31104a(11) =7776a(12) =186624a(13) =46656a(14) =1119744a(15) =279936a(16) =6718464a(17) =1679616a(18) =40310784a(19) =10077696a(20) =241864704a(21) =60466176a(22) =1451188224a(23) =362797056a(24) =8707129344a(25) =2176782336a(26) =52242776064a(27) =13060694016a(28) =313456656384a(29) =78364164096