Primes of the form $a^2+b^2+c^2$, $0<a<b<c$

133 Views Asked by At

Are there results showing which prime numbers that can be expressed as the sum of three different integers greater than zero?


By the three square theorem of Legendre a natural number can be written as a square sum of three natural numbers if and only if it isn't of the form $4^i(8j+7)$. where $i,j$ are natural numbers.

Due to an answer to Conjecture: Any sufficiently big sum of three squares can be written as a square sum of three different natural numbers greater than zero there is a conjecture by Jeffrey Shallit:

A number is a sum of 3 squares, but not a sum of 3 distinct nonzero squares, if and only if it is of the form $4^js$, where $j \ge 0$ and

$s \in$
{1, 2, 3, 5, 6, 9, 10, 11, 13, 17, 18, 19, 22, 25, 27, 33, 34, 37, 43, 51, 57, 58, 67, 73, 82, 85, 97, 99, 102, 123, 130, 163, 177, 187, 193, 267, 627, 697}

So, if the conjecture by Shallit is true, then all primes not of the form $8m+7$ and not belonging to $\{2, 3, 5, 11, 13, 17, 19, 37, 43, 67, 73, 97, 163, 193\}$ can be written as a square sum of three different non zero natural numbers.

1

There are 1 best solutions below

0
On BEST ANSWER

Nothing seems be known. See OEIS/A125516. Contrast with OEIS/A085317.