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Triangular Square Numbers: a Postscript

The article by Mr. D. C. D. Potter in Gazette LVI, No. 396 (May 1972), pp. 109-10 attracted a number of interesting letters. We cannot print all of these in full, but the main points are included in the following extracts. First, Dr. K. Szymiczek of the Silesian University, Katowice, Poland (writing from Cambridge) offered some information on the history of the problem. “According to L. E. Dickson, L. Euler was the first to show that there are infinitely many square triangular numbers and S. Roberts proved in 1879 that Euler's formula gives all square triangular numbers ([1], pp. 13, 27).”