To be proper camel case (with digits allowed) a word:

• MUST start with a lower case alphabet (a through z)
• MUST have no spaces, punctuation or special characters
• CAN have at most 1 uppercase alphabet in a row
• MAY end in an uppercase alphabet
• MAY contain digits 0 - 9

Notable examples

• cP3 is valid lower camel case (with digits allowed)
• a1 is valid lower camel case (with digits allowed)
• a1G is valid lower camel case (with digits allowed)
• a123 is valid lower camel case (with digits allowed)
• camelCa1 is valid lower camel case (with digits allowed)
• camel01C is valid lower camel case (with digits allowed)