Very good, you got it. We're still missing 3 clues. Lines 3 and 9 are incorrect, and missing one on line 4. — Jack Pettinger 1 min ago

Please can you edit to explain this answer? It's not enough to say the clues "made good sense" - you need to explain why. Answers without explanation are liable to be removed. — Rand al'Thor 34 secs ago

Also, this answer was already mentioned before... Answers should add something new, and not be just 'I know the answer, too!' — Glorfindel 1 min ago

Yes, it is Russian for two. :) — Mic Crozier 1 min ago

No need to post multiple answers - you can always edit your original post. (Also, for the record someone else already HAS answered, and his answer has been marked as correct, three years ago.) — Rand al'Thor 24 secs ago

Please explain why you think this is the case... — Beastly Gerbil 30 secs ago

I think @Kriti is splitting the sequence up into three component parts: 20,21 ; 21,22 ; 12,13, where the second number of each part is the increase of the first respectively. — Tarius 1 min ago