The sender is sending ASCII data. The mapped pot reading is output one character at a time.
The receiver has some bizarre idea that the sender has sent an int, and that the reading, storing, and conversion of the character to an int happens automagically. Here's a clue. It doesn't.
What you are getting is not 10, 49, 54, 13 repeated. It's 45, 54, 13, 10. The 49 is the ASCII code for a 1. 54 is the ASCII code for 6. The 13 and 10 are carriage return and line feed (that println() added).