I've known the following theorem.
Theorem: Supposing that an+1=⌊1.05×an⌋ for any natural number n, there exists N such that aN≡0 (mod 10) for any integer 20≤a1≤100.
Proof: {an} is a monotonic increase sequence, so let's observe the minimum n such that an≥100 for any a1. The observation shows you that you'll always get any one of 100,101,102,103. Then, you get 101→106→111→116→121→127→133→139→145→152→159→166→174→182→191→200
102→107→112→117→122→128→134→140
103→108→113→118→123→129→135→141→148→155→162→170,
Then, here are my questions.
As far as I know, the next question still remains unsolved.
Question1: Supposing that an+1=⌊1.05×an⌋ for any natural number n, does there exist N such that aN≡0 (mod 10) for any integer a1≥20 ?
It is likely that such N would exist, but I'm facing difficulty.
I'm also interested in the following generalization.
Question2: Supposing that α>1 is a real number and that an+1=⌊α×an⌋ for any natural number n, does there exist N such that aN≡0 (mod 10) for any integer a1≥1α−1 ?
Any help would be appreciated.
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