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.
re: No primes here (spoiler) .... a typo
