What is the 25th number in the pattern: 1, 2, 3, 5, 7, 10, 13, 17, 21, 26 …?

We have:

1+1=2

2+1=3

3+2=5

5+2=7

7+3=10

10+3=13

13+4=17

17+4=21

21+5=26

...

So the 25th number is:26+5+6+6+7+7+8+8+9+9+10+10+11+11+12+12=157

Answer: 157