Odd values of n for which a regular n-gon can be constructed by compass and straightedge.

Terms

a(0) =3a(1) =5a(2) =15a(3) =17a(4) =51a(5) =85a(6) =255a(7) =257a(8) =771a(9) =1285a(10) =3855a(11) =4369a(12) =13107a(13) =21845a(14) =65535a(15) =65537a(16) =196611a(17) =327685a(18) =983055a(19) =1114129a(20) =3342387a(21) =5570645a(22) =16711935a(23) =16843009a(24) =50529027a(25) =84215045a(26) =252645135a(27) =286331153a(28) =858993459a(29) =1431655765