lean_workbook_plus_15734

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by Community (Bot) · Feb 28, 2026 · Mathlib 777aaa6 (Lean v4.29.0-rc3)

Prove that if $S(n)$ is the sum of decimal digits of a positive integer $n$ , then $S(n) \equiv n \pmod{9}$ .

Preamble

import Mathlib.Analysis.Complex.Basic

Formal statement

theorem lean_workbook_plus_15734 (n : ℕ) : (Nat.digits 10 n).sum % 9 = n % 9   :=  by sorry

Source