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In page Goldbach's conjecture:

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where the product is over all primes p, and γc,p(n) is the number of solutions to the equation n = q1 + ⋯ + qc mod p in modular arithmetic, subject to the constraints q1, …, qc ≠ 0 mod p. This formula has been rigorously proven to be asymptotically valid for c ≥ 3 from the work of Ivan Matveevich Vinogradov, but is still only a conjecture when c = 2.[citation needed] In the latter case, the above formula simplifies to 0 when n is odd, and to