196-Algorithm Program
Why bother renaming a to b?

This function would be more useful as a generator, because you will be interested in finding the next number in the sequence.  That is, you should yield rather than return the result.

You wrote str(b) three times.  Once would be better, but that would still be once too many, if you care about performance.  Keep in mind that stringifying a number involves allocating an object, some buffer space, some arithmetic, and translation to ASCII behind the scenes.  A function to compute the reversed integer yourself, even if it involves writing more code, should be faster.