Unlike other social networking sites lke Facebook and Twitter, Google+ doesn’t offer vanity URLs for user profiles, making it more difficult to share your Google+ Profile. Instead, Google uses a long string of numbers to denote users (e.g. 117679391504351387685).
The reason Google+ doesn’t use vanity URLs is because those could lead to spammers figuring out the email addresses of Google+ users (as many Google Accounts are linked to Gmail accounts).