Lonely Numbers

Given a number, insert duplicate digits on both sides of all digits which appear in a group of 1.

Worked Example

numbers_need_friends_too(22733) ➞ 2277733

# The number can be split into groups 22, 7, and 33.
# 7 appears on its own.
# Put 7s on both sides to create 777.
# Put the numbers together and return the result.

Examples

numbers_need_friends_too(123) ➞ 111222333

numbers_need_friends_too(56657) ➞ 55566555777

numbers_need_friends_too(33) ➞ 33

Notes

All tests will include positive integers.