Journal of Integer Sequences, Vol. 24 (2021), Article 21.9.3

The Number a2 + b2dc2 Revisited

Nguyen Viet Dung and Luu Ba Thang
Department of Mathematics and Informatics
Hanoi National University of Education
136 Xuan Thuy
Cau Giay, Hanoi


In 2015, Nowicki posed the following question: let d = q or d = 2q, where q is a product of prime numbers of the form 4k + 1. Is it true that d is a special number? We answer this open question.

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Received April 27 2021; revised version received September 27 2021. Published in Journal of Integer Sequences, October 1 2021.

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