a(0) = 1, a(n) = a(n - 1) * (length of binary representation of n).

Terms

a(0) =1a(1) =1a(2) =2a(3) =4a(4) =12a(5) =36a(6) =108a(7) =324a(8) =1296a(9) =5184a(10) =20736a(11) =82944a(12) =331776a(13) =1327104a(14) =5308416a(15) =21233664a(16) =106168320a(17) =530841600a(18) =2654208000a(19) =13271040000a(20) =66355200000a(21) =331776000000