a(n) = round(tan(Pi*(1-1/n)/2)).

Terms

a(0) =0a(1) =1a(2) =2a(3) =2a(4) =3a(5) =4a(6) =4a(7) =5a(8) =6a(9) =6a(10) =7a(11) =8a(12) =8a(13) =9a(14) =10a(15) =10a(16) =11a(17) =11a(18) =12a(19) =13a(20) =13a(21) =14a(22) =15a(23) =15a(24) =16a(25) =17a(26) =17a(27) =18a(28) =18a(29) =19