numbers which do not make pairs are called
Friendly number A number that is not part of any friendly pair is called solitary.
Nibble In computing, a nibble (occasionally nybble or nyble to match the spelling of byte) is a four-bit aggregation,[1][2] or half an octet. It is also known as half-byte[3] or tetrade.[4][5] In a networking or telecommunication context, the nibble is often called a semi-octet,[6] quadbit,[7] or quartet.[8][9] A nibble has sixteen (24) possible values. A nibble can be represented by a single hexadecimal digit and called a hex digit.[10]