21042491 has 2 divisors, whose sum is σ = 21042492. Its totient is φ = 21042490.

The previous prime is 21042479. The next prime is 21042533. The reversal of 21042491 is 19424012.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21042491 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21032491) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10521245 + 10521246.

It is an arithmetic number, because the mean of its divisors is an integer number (10521246).

Almost surely, 2^21042491 is an apocalyptic number.

21042491 is a deficient number, since it is larger than the sum of its proper divisors (1).

21042491 is an equidigital number, since it uses as much as digits as its factorization.

21042491 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 576, while the sum is 23.

The square root of 21042491 is about 4587.2095003390. The cubic root of 21042491 is about 276.0783707640.

The spelling of 21042491 in words is "twenty-one million, forty-two thousand, four hundred ninety-one".