Approximate Probability of/odds against
Two distinct people having the same birthday in a crowd of N people

  N      probability    odds
  1             0       infinity
  2       2.739726E-3   364.000    
  3       8.204166E-3   120.889    
  4       1.635591E-2   60.1400    
  5       2.713557E-2   35.8520    
  6       4.046248E-2   23.7143    
  7       5.623570E-2   16.7823    
  8       7.433529E-2   12.4526    
  9       9.462383E-2   9.56816    
 10      0.116948       7.55080    
 11      0.141141       6.08509    
 12      0.167025       4.98714    
 13      0.194410       4.14376    
 14      0.223103       3.48224    
 15      0.252901       2.95411    
 16      0.283604       2.52604    
 17      0.315008       2.17453    
 18      0.346911       1.88258    
 19      0.379119       1.63770    
 20      0.411438       1.43050    
 21      0.443688       1.25383    
 22      0.475695       1.10219    
 23      0.507297      0.971231    
 24      0.538344      0.857547    
 25      0.568700      0.758397    
 26      0.598241      0.671568    
 27      0.626859      0.595254    
 28      0.654461      0.527974    
 29      0.680969      0.468497    
 30      0.706316      0.415796    
 31      0.730455      0.369010    
 32      0.753348      0.327409    
 33      0.774972      0.290369    
 34      0.795317      0.257360    
 35      0.814383      0.227923