MySQL solution , but first explanation of algorithm.

WITH RECURSIVE t AS (
    SELECT 2 AS nums
    UNION
    SELECT nums + 1
    FROM t
    WHERE nums < 1000
)
SELECT GROUP_CONCAT(nums SEPARATOR '&')
FROM t
WHERE nums NOT IN (
    SELECT a.nums
    FROM t a
    JOIN t b ON b.nums <= FLOOR(SQRT(a.nums)) AND a.nums % b.nums = 0
);

• The logic presented in the condition b.nums <= FLOOR(SQRT(a.nums)) AND a.nums % b.nums = 0 can be considered as part of an algorithm to find prime numbers. Specifically, it is part of the Sieve of Eratosthenes algorithm for finding all prime numbers up to a given number.

• The Sieve of Eratosthenes is an ancient and efficient algorithm for finding all prime numbers up to a specified integer. It works by iteratively marking the multiples of each prime number as composite (non-prime), starting from 2, which is the first prime number. The algorithm progressively eliminates multiples of each prime number, and the remaining unmarked numbers are prime.

• The logic in the condition serves the purpose of identifying composite (non-prime) numbers efficiently. For each number a.nums generated by the CTE t, it checks for divisors (b.nums) up to the square root of a.nums. If a.nums is found to be divisible by any number other than 1 and itself (leaving a remainder of 0), then it is marked as composite (non-prime).

• • By employing this condition within the context of the Sieve of Eratosthenes algorithm, the query effectively finds all prime numbers up to a given limit.