Nonnegative multiples of 6.

Terms

a(0) =0a(1) =6a(2) =12a(3) =18a(4) =24a(5) =30a(6) =36a(7) =42a(8) =48a(9) =54a(10) =60a(11) =66a(12) =72a(13) =78a(14) =84a(15) =90a(16) =96a(17) =102a(18) =108a(19) =114a(20) =120a(21) =126a(22) =132a(23) =138a(24) =144a(25) =150a(26) =156a(27) =162a(28) =168a(29) =174