Inverse Colombian function.

Terms

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