What is the missing number for the sequel 1 2 5 10 13 blank

{a: a∈N ∧ a = x² + y²} = {1, 2, 5, 10, 13, 17, ...}

Offset 1, 2

1² + 2² = 1 + 4 = 5
1² + 3² = 1 + 9 = 10
2² + 3² = 4 + 9 = 13
1² + 4² = 1 + 16 = 17

He was paid 23 dollars for each lawn