Assuming the digits 0 through 7(N=8) is the most frequent subset, then one can infer 'the most frequent pairs' below. Cost and waging strategy is how you deal with the conditions below.
Condition 1>640 picks
{0,0} {0,1} {0,2} {0,3} {0,4} {0,5} {0,6} {0,7} {1,0} {1,1} {1,2} {1,3} {1,4} {1,5} {1,6} {1,7} {2,0} {2,1} {2,2} {2,3} {2,4} {2,5} {2,6} {2,7} {3,0} {3,1} {3,2} {3,3} {3,4} {3,5} {3,6} {3,7} {4,0} {4,1} {4,2} {4,3} {4,4} {4,5} {4,6} {4,7} {5,0} {5,1} {5,2} {5,3} {5,4} {5,5} {5,6} {5,7} {6,0} {6,1} {6,2} {6,3} {6,4} {6,5} {6,6} {6,7} {7,0} {7,1} {7,2} {7,3} {7,4} {7,5} {7,6} {7,7}
Condition 2>560 picks
{0,1} {0,2} {0,3} {0,4} {0,5} {0,6} {0,7} {1,0} {1,2} {1,3} {1,4} {1,5} {1,6} {1,7} {2,0} {2,1} {2,3} {2,4} {2,5} {2,6} {2,7} {3,0} {3,1} {3,2} {3,4} {3,5} {3,6} {3,7} {4,0} {4,1} {4,2} {4,3} {4,5} {4,6} {4,7} {5,0} {5,1} {5,2} {5,3} {5,4} {5,6} {5,7} {6,0} {6,1} {6,2} {6,3} {6,4} {6,5} {6,7} {7,0} {7,1} {7,2} {7,3} {7,4} {7,5} {7,6}
Condition 3>280 picks
{0,1} {0,2} {0,3} {0,4} {0,5} {0,6} {0,7} {1,2} {1,3} {1,4} {1,5} {1,6} {1,7} {2,3} {2,4} {2,5} {2,6} {2,7} {3,4} {3,5} {3,6} {3,7} {4,5} {4,6} {4,7} {5,6} {5,7} {6,7}
Start testing each condition, then decide your waging strategy, don't look at total picks for each condition, it will dissuade you from seeing the lager picture(most frequent digits infer most frequent pairs). The above picks can be reduced 10 to 64 picks using just the sum parameter.
Prediction>filter digits 5 and 6 as lead digits from the above conditions.