Charles Ellicott Commentary 1 Chronicles 7:16

"And Maacah the wife of Machir bare a son, and she called his name Peresh; and the name of his brother was Sheresh; and his sons were Ulam and Rakem." — 1 Chronicles 7:16 (ASV)

Peresh ... Sheresh occur nowhere else.

Ulam and Rakem (Rekem) were probably sons of the elder, Peresh, whose line would naturally be continued, as usual.