Interesting numbers

Let n be a number with 2d digits. Let a be the first d digits of this number and b the last d digits. For example: n=140400 d=3 a=140 b=400 This number has an interesting property such that n = b² - a² How many numbers less than 10⁵⁰ have this interesting property? Answer format: cnt,∑n [My timing: ~2s]