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Zagier, D. (1990) A One-Sentence Proof That Every Prime p ≡ 1 (mod 4) Is a Sum of Two Squares. The American Mathematical Monthly, 97, 144-144.
https://doi.org/10.1080/00029890.1990.11995565

has been cited by the following article:

• TITLE: A Sufficient Condition for the Primality of the Sum of Two Squares

  AUTHORS: Han-Lin Li, Shu-Cherng Fang, Way Kuo

  KEYWORDS: Fermat, Brahmagupta-Fibonacci Identity, Primality

  JOURNAL NAME: Advances in Pure Mathematics, Vol.16 No.6, June 11, 2026

  ABSTRACT: The famous Fermat’s Christmas Theorem states that all Pythagorean primes can be expressed as a sum of two squares of integers. This report specifies the conditions that a ( 4k+1 )-type integer expressed in a sum of two squares becomes prime.