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Triangular quartet

The first four triangular numbers are 1, 3, 6 and 10, and the nth triangular number is given by the expression n(n+1)/2, so the 20th such number is 20 × 21 ÷ 2 = 210.

ENIGMA is a triangular number in which all the digits are different. ENI – GMA = MM, and each of ENI, GMA and MM is a triangular number.

Find ENIGMA.

WIN £15 will be awarded to the sender of the first correct answer opened on Tuesday 24 May. The Editor’s decision is final. Please send entries to Enigma 1642, New Å®ÉúСÊÓƵ, Lacon House, 84 Theobald’s Road, London WC1X 8NS, or to enigma@newscientist.com (please include your postal address).

Answer to 1636 Risky business: 4 per cent had the bug

The winner David Gilbert of Point Howard, New Zealand