**From New Scientist #2549, 29th April 2006**

Put a digit in each square of a three-by-three grid so that there are three three-digit numbers across and three three-digit numbers down. The sum of the digits of each of the six numbers must be the same.

The “across” numbers must be three different triangular numbers. Triangular numbers are those that fit the formula n(n+1)/2, like 1, 3, 6, 10, 15. Your numbers must not start with a zero.

List your three triangular numbers in ascending order.

[enigma1389]

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Solution:The three triangular numbers are 276, 528 and 861.