Cyclic Difference Set (83, 41, 20)

    1     3     4     7     9    10    11    12    16    17    21    23
   25    26    27    28    29    30    31    33    36    37    38    40
   41    44    48    49    51    59    61    63    64    65    68    69
   70    75    77    78    81