21523591 has 2 divisors, whose sum is σ = 21523592. Its totient is φ = 21523590.

The previous prime is 21523589. The next prime is 21523609. The reversal of 21523591 is 19532512.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21523591 - 2¹ = 21523589 is a prime.

Together with 21523589, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21523511) 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, 10761795 + 10761796.

It is an arithmetic number, because the mean of its divisors is an integer number (10761796).

Almost surely, 2^21523591 is an apocalyptic number.

21523591 is a deficient number, since it is larger than the sum of its proper divisors (1).

21523591 is an equidigital number, since it uses as much as digits as its factorization.

21523591 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2700, while the sum is 28.

The square root of 21523591 is about 4639.3524332605. The cubic root of 21523591 is about 278.1665539225.

The spelling of 21523591 in words is "twenty-one million, five hundred twenty-three thousand, five hundred ninety-one".