A problem in Project Euler

Question

Hi guys,I Have just discovered the site "Project Euler" and it's fun and really challenging but I have a serious problem with a few of its math problems:
It says: Find the largest number that is the sum of 3 triangle numbers.
What does it mean the largest number???!
We don't have such number! it's indefinite!

Answer 1

In problem 41,
the largest number cannot be more than 9 digits.
You cannot use the same digit more than once, so 987654321 is okay, but 9986651.. is not. So the answer is not indefinite.

The twist to this challenge is that you have to find the largest one that is a prime.
987654321 is not a prime, so that can't be the largest pandigital number.
(0 is excluded).

Answer 2

What was the Problems ID number?
(Just so I can check if there's restrictions to the numbers size, and what a triangle number is)

Answer 3

Problem 41 for example

Answer 4

for example 3,4,5 are three triangle numbers

Answer 5

Thanks a lot.