Nth root calculator

Most calculators refuse the cube root of a negative number because they compute roots through logarithms, and the logarithm of a negative number does not exist. This tool takes the real branch instead: the root of the absolute value with the sign restored for odd indices. Even roots of negative numbers have no real answer, and the tool says so rather than printing NaN. Where the root is irrational, the result carries every digit a double can hold, no more: the round-trip check below shows whether raising the answer back to the index lands exactly on your input.