Sectors on dartboard.

Terms

a(0) =1a(1) =18a(2) =4a(3) =13a(4) =6a(5) =10a(6) =15a(7) =2a(8) =17a(9) =3a(10) =19a(11) =7a(12) =16a(13) =8a(14) =11a(15) =14a(16) =9a(17) =12a(18) =5a(19) =20a(20) =25a(21) =50