a(n) = lcm{1 <= k <= n, gcd(k, 3) = 1}.

Terms

a(0) =1a(1) =1a(2) =2a(3) =2a(4) =4a(5) =20a(6) =20a(7) =140a(8) =280a(9) =280a(10) =280a(11) =3080a(12) =3080a(13) =40040a(14) =40040a(15) =40040a(16) =80080a(17) =1361360a(18) =1361360a(19) =25865840a(20) =25865840a(21) =25865840a(22) =25865840a(23) =594914320a(24) =594914320a(25) =2974571600a(26) =2974571600a(27) =2974571600a(28) =2974571600a(29) =86262576400