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Euler's 6n+1 Theorem


Euler's 6n+1 theorem states that every prime of the form 6n+1, (i.e., 7, 13, 19, 31, 37, 43, 61, 67, ..., which are also the primes of the form 3n+1; OEIS A002476) can be written in the form x^2+3y^2 with x and y positive integers.

The first few positive integers that can be represented in this form (with x,y>0) are 4, 7, 12, 13, 16, 19, ... (OEIS A092572), summarized in the following table together with their representations.

n(x,y)
4(1, 1)
7(2, 1)
12(3, 1)
13(1, 2)
16(2, 2)
19(4, 1)
21(3, 2)
28(1, 3), (4, 2), (5, 1)
31(2, 3)

Restricting solutions such that (x,y)=1 (i.e., x and y are relatively prime), the numbers that can be represented as x^2+3y^2 are 4, 7, 12, 13, 19, 21, 28, 31, 37, 39, 43, ... (OEIS A092574), as summarized in the following table.

n(x,y) with (x,y)=1
4(1, 1)
7(2, 1)
12(3, 1)
13(1, 2)
19(4, 1)
21(3, 2)
28(1, 3), (5, 1)
31(2, 3)
37(5, 2)

See also

Diophantine Equation--2nd Powers, Fermat's Theorem, Prime Number

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References

Sloane, N. J. A. Sequences A002476/M4344, A092572, A092573, A092574, and A092575 in "The On-Line Encyclopedia of Integer Sequences."

Referenced on Wolfram|Alpha

Euler's 6n+1 Theorem

Cite this as:

Weisstein, Eric W. "Euler's 6n+1 Theorem." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Eulers6nPlus1Theorem.html

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