Fermat number
In July 1999 – while a participant in the Proth Search Group – he became the discoverer of the then-largest known composite Fermat number, a record which his St. Patrick's College (Drumcondra) based Proth-Gallot Group twice broke in 2003, the 1999 record having stood until then. The third of those records continued to stand until it was broken in June 2011.