| j ≤ i, 0 < i, 0 < j, fac(i - j) * fac(j) | fac(i), fac(i + 1 - j) * fac(j - 1) | fac(i), 0 ≤ j, 0 ≤ i ⊦ (fac(i) / (fac(i - j) * fac(j)) - fac(i) / (fac(i + 1 - j) * fac(j - 1))) * fac(j) * fac(i + 1 - j) = fac(i) * (i + 1 - 2 * j) |
⊦ (i - j) * j0 = i * j0 - j * j0
j ≤ i, 0 < i, 0 < j, fac(i - j) * fac(j) | fac(i), fac(i + 1 - j) * fac(j - 1) | fac(i), 0 ≤ j, 0 ≤ i ⊦ fac(i) / (fac(i - j) * fac(j)) * fac(j) * fac(i + 1 - j) - fac(i) / (fac(i + 1 - j) * fac(j - 1)) * fac(j) * fac(i + 1 - j) = fac(i) * (i + 1 - 2 * j)
Used terms: fac(j) * fac(i + 1 - j), fac(i) / (fac(i + 1 - j) * fac(j - 1)), fac(i) / (fac(i - j) * fac(j))