Useful mathematical concepts, like the number line, can linger for millennia before they are rigorously defined.

"It can calculate the square root of a 10-bit binary number (within the decimal integer 900) by designing DNA sequences and programming DNA strand displacement reactions," the paper reads.

This means they are made of both real numbers and the imaginary number i: the square root of negative 1. Remember, a square root of a number represents a number whose square is the original number.