Chromatic number (or Heawood number) Chi(n) of surface of genus n.

Terms

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