21523991 has 2 divisors, whose sum is σ = 21523992. Its totient is φ = 21523990.

The previous prime is 21523969. The next prime is 21524029. The reversal of 21523991 is 19932512.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21523991 - 2⁶ = 21523927 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21523961) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10761995 + 10761996.

It is an arithmetic number, because the mean of its divisors is an integer number (10761996).

Almost surely, 2^21523991 is an apocalyptic number.

21523991 is a deficient number, since it is larger than the sum of its proper divisors (1).

21523991 is an equidigital number, since it uses as much as digits as its factorization.

21523991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 4860, while the sum is 32.

The square root of 21523991 is about 4639.3955425249. The cubic root of 21523991 is about 278.1682770850.

The spelling of 21523991 in words is "twenty-one million, five hundred twenty-three thousand, nine hundred ninety-one".