21075991 has 2 divisors, whose sum is σ = 21075992. Its totient is φ = 21075990.

The previous prime is 21075979. The next prime is 21076019. The reversal of 21075991 is 19957012.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21075991 - 2⁷ = 21075863 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21075931) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10537995 + 10537996.

It is an arithmetic number, because the mean of its divisors is an integer number (10537996).

Almost surely, 2^21075991 is an apocalyptic number.

21075991 is a deficient number, since it is larger than the sum of its proper divisors (1).

21075991 is an equidigital number, since it uses as much as digits as its factorization.

21075991 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 5670, while the sum is 34.

The square root of 21075991 is about 4590.8595055828. The cubic root of 21075991 is about 276.2248002238.

The spelling of 21075991 in words is "twenty-one million, seventy-five thousand, nine hundred ninety-one".