Chromatic number (or Heawood number) of nonorientable surface with n crosscaps.

Terms

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