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I have been looking at some simpler versions where digits sum < 9 example: from 1 to $10^4$ how many sum to 5? using repeated combinations $$\binom{5+5−1}{5}=\binom{9}{5}=126$$ however the given answer is 56

does a generalized version (formula) exist where R = sum of digits ; N = number of digits. $$ A \leq N \leq B $$

in the example above$$ R = 5; N = 5; A = 1; B = 5; $$

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