PHP (at least old versions I worked with) treats "65537" and 65537 similarly.

That sounds horrible if you want to transmit a base64 string where the length is a multiple of 3 and for some cursed reason there's no letters or special characters involved. If "7777777777777777" is your encoded string because you're sending a string of periods encoded in BCD, you're going to have a fun time. Perhaps that's karma for doing something braindead in the first place though.