21539591 has 2 divisors, whose sum is σ = 21539592. Its totient is φ = 21539590.

The previous prime is 21539519. The next prime is 21539593. The reversal of 21539591 is 19593512.

Together with previous prime (21539519) it forms an Ormiston pair, because they use the same digits, order apart.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21539591 - 2¹⁰ = 21538567 is a prime.

Together with 21539593, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21539593) 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, 10769795 + 10769796.

It is an arithmetic number, because the mean of its divisors is an integer number (10769796).

Almost surely, 2^21539591 is an apocalyptic number.

21539591 is a deficient number, since it is larger than the sum of its proper divisors (1).

21539591 is an equidigital number, since it uses as much as digits as its factorization.

21539591 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 12150, while the sum is 35.

The square root of 21539591 is about 4641.0764915050. The cubic root of 21539591 is about 278.2354637757.

The spelling of 21539591 in words is "twenty-one million, five hundred thirty-nine thousand, five hundred ninety-one".