(Regarding the numbers in Surat Alfateha:  7 ayats, 29 words, 139 letters)

Theorem:

7ⁿ + 29ⁿ + 139ⁿ is always a composite number for every n. Proof. Note that 29 + 139 = 168 = 7 × 24, hence for odd number n, 29ⁿ + 139ⁿ has a factor 29 + 139. Thus the result holds. So we assume n = 2k.Let

φ(k) = 7^2k + 29^2k + 139^2k = 49^k + 841^k + 19321^k .

Note that

49 ≡ 1(mod 3),

841 ≡ 1(mod 3),

19321 ≡ 1(mod 3),

then

49k ≡ 1(mod 3),

841k ≡ 1(mod 3),

19321k ≡ 1(mod 3).

Therefore, 49^k + 841^k + 19321^k ≡ 3(mod 3), that is 3|49^k + 841^k + 19321^k .