Google told me to look in the papers:

Triangular Numbers and Perfect Squares

Tom Beldon and Tony Gardiner

The Mathematical Gazette

Vol. 86, No. 507 (Nov., 2002), pp. 423-431

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88.53 Comments on 'Triangular Numbers and Perfect Squares'

Michael D. Hirschhorn

The Mathematical Gazette

Year, volume, issue, and the page range: Vol. 88, No. 513 (Nov., 2004), pp. 500-503

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