Thread: Formula for the nth palindromic number?

I was just wondering if there's a formula for the nth palindromic number in base 10?

Thanks in advance!

do you mean pascal's triangle?
1
1,1
1,2,1
1,3,3,1
1,4,6,4,1
1,5,10,10,5,1
1,6,15,20,15,6,1
1,7,21,35,35,21,7,1
1,8,28,56,70,56,28,8,1
1,9,36,84,126,126,84,36,9,1
1,10,45,120,210,252,210,120,45,10,1
If so, then here's a formula.

Plaindromic, so like 1, 11, 131, 2552, etc?

Well, you can just break it in half and count up each half. Skipping 0:
- The first 9: 1, 2, ..., 9
- The next 9: 11, 22, ..., 99
- The next 90: 101, 111, 121, ..., 999
- etc.

So yeah, that could be generalized. You'd get something more like an algorithm than a formula unless you were very careful about it though.