Question

In the Pythagorean triplet 9,40,41 what is the natural number

Answer 1

A Pythagorean triple consists of three positive integers a, b, and c, such that a2 + b2 = c2. ... The name is derived from the Pythagoreantheorem, stating that every right triangle has side lengths satisfying the formula a2 + b2 = c2; thus, Pythagorean triples describe the three integer side lengths of a right triangle
we know that from your question
the triplet is
9,40,41
and we have definition of
Natural numbers, also called counting numbers, are the numbers used for counting things. Sometimes the special number zero is called a natural number. Sometimes one is called the smallest natural number. Natural numbers are always whole numbers (integers) and never less than zero.
by definition 9,40,41
all are natural numbers

also note that 9 is the only one perfect square in this