I just want to express my upmost gratitude for 22i sensei. An open end is the only perfect way to end such a wholesome series, so thank you so much, I loved it a lot. I'm definitely going to have this manga series on my wish list to buy before I die.
Okay I didn't mean to look like I didn't cared about Marika (I'm really sad tbh, with the previous foreshadowing and such), but I got worked up and solved the problem before continuing with the following pages...
Given that the sequence an is the sequence of the ones digit of 3n, find the smallest positive integer A satisfying an+A = an for all positive integer n.
Lemma: Given that a ≡ c (mod n) and b ≡ d (mod n), then ab ≡ cd (mod n)
Proof: a ≡ c (mod n) and b ≡ d (mod n) implies a-c = pn and b-d = qn...