a(n) = 6*a(n-2) for n > 2; a(1) = 1, a(2) = 5.

Terms

a(0) =1a(1) =5a(2) =6a(3) =30a(4) =36a(5) =180a(6) =216a(7) =1080a(8) =1296a(9) =6480a(10) =7776a(11) =38880a(12) =46656a(13) =233280a(14) =279936a(15) =1399680a(16) =1679616a(17) =8398080a(18) =10077696a(19) =50388480a(20) =60466176a(21) =302330880a(22) =362797056a(23) =1813985280a(24) =2176782336a(25) =10883911680a(26) =13060694016a(27) =65303470080a(28) =78364164096