Let:

F[n]= Sum[n - i*j, {i, 1, n}, {j, 1, n/i}]

n is prime if and only if:

F[n + 1] - 2F[n] + F[n - 1]=2

More:

F[n + 1] - 2F[n] + F[n - 1]=d(n)

Sincerely

Sebastian Martin Ruiz

[Non-text portions of this message have been removed]

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Let:

F[n]= Sum[n - i*j, {i, 1, n}, {j, 1, n/i}]

n is prime if and only if:

F[n + 1] - 2F[n] + F[n - 1]=2

More:

F[n + 1] - 2F[n] + F[n - 1]=d(n)

Sincerely

Sebastian Martin Ruiz

[Non-text portions of this message have been removed]