A₀ = N mod 9
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Ankerwaarde
Digital Root
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dr(N) = A₀
Optimal Payment (Greedy — provably optimal) Canonical
Total Payment Ways (15 denominations) O(1)
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Reduction Chain N → digit sum → … → dr(N)
Stelselparameters (p, q, r, s, t) — randvoorwaarden: p ≡ 1 (mod q) & t | s | r | q