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'Thor34 secs 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'Thor24 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. — Tarius1 min ago