Index cell where number jumps

I'm trying to identify the cell where the numbers jumps drastically...

example:

[1 2 3 4 5 6 20 21 22 23 24 25 60 61 62 63 64 65]

How do I indentify the index where 6 and 25 stop in the section of increasing numbers and the new section of increasing numbers continues.

Thanks for your help!

Answer 1

[Fangjun Jiang]

A=[1 2 3 4 5 6 20 21 22 23 24 25 60 61 62 63 64 65]
B=diff(A)
find(B>1)