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Integers below a million with digit sum 19

Question

Count the positive integers less than 1,000,0001{,}000{,}000 whose decimal digits add up to 1919.

Short answer

30492=(245)−6(145)30492=\binom{24}{5}-6\binom{14}{5}. Pad to six digits d1+⋯+d6=19d_1+\dots+d_6=19 with 0≤di≤90\le d_i\le 9. Stars and bars gives (245)\binom{24}{5} without the cap; a digit exceeding 99 can happen for only one digit at a time (two would need 2020), and each such case leaves (145)\binom{14}{5} solutions, so subtract 6(145)6\binom{14}{5}.

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