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Oh, dude, triangular numbers are like the cool kids of math, they're all about those equilateral vibes. So, between 11 and 39, we've got 15 and 21 as triangular numbers. That's it, just those two. It's like a tiny exclusive club, you know?
There are 6 numbers between 1 and 70 that are divisible by 11. These numbers are: 11; 22; 33; 44; 55; 66.
There are 90 such numbers.
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If you are including 10 and 30 there are 11 even numbers. If you are not counting 10 and 30 there are 9 even numbers between 10 and 30.