Prove that no number in the sequence 949, 9449, 94449... is prime.

(In reply to

No primes here (spoiler) by Steve Herman)

Good reasoning and a correct answer.

Just change **1 into 5** to fix a small typo:

......'Trying 7 and 37 as factors of 9444449, we find that 9444449 = 7*1349207. If the number of **4's (mod 6) = 1,** then it is therefore a multiple of 7. (We could prove this by calculating divisors mod 7 of 10^n, which necessarily repeat with period 6.)"

...for the benefit of other readers.