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Saturday, April 27, 2024

2024/032) What is the proof that 11 is the only prime number of the form n^2 + 2 where n is prime?

We have a prime number is 2 or 3 of of the form 6n\pm  1 for n \gt 0 let us compute n^2+2

2^2 + 2 = 6 = 2 * 3 not a prime

3^2+ 2  = 11 is a prime

(6n\pm  1)^2+ 2 = (36n^2 \pm 12 n + 1) + 2 =  (36n^2 \pm 12 n + 3)  = 3(12n^2 \pm 4 n + 1) which is not a prime

hence 11 is the only prime

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