Multiples of 20.

Terms

a(0) =0a(1) =20a(2) =40a(3) =60a(4) =80a(5) =100a(6) =120a(7) =140a(8) =160a(9) =180a(10) =200a(11) =220a(12) =240a(13) =260a(14) =280a(15) =300a(16) =320a(17) =340a(18) =360a(19) =380a(20) =400a(21) =420a(22) =440a(23) =460a(24) =480a(25) =500a(26) =520a(27) =540a(28) =560a(29) =580