The (6^n)-th composite number.

Terms

a(0) =4a(1) =12a(2) =52a(3) =275a(4) =1539a(5) =8883a(6) =51974a(7) =306464a(8) =1815791a(9) =10791313a(10) =64266028a(11) =383289080a(12) =2288430270a(13) =13674181949a(14) =81759268145a(15) =489087871679