21539949 has 4 divisors (see below), whose sum is σ = 28719936. Its totient is φ = 14359964.

The previous prime is 21539933. The next prime is 21539971. The reversal of 21539949 is 94993512.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21539949 - 2⁴ = 21539933 is a prime.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21539949.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21539149) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3589989 + ... + 3589994.

It is an arithmetic number, because the mean of its divisors is an integer number (7179984).

Almost surely, 2^21539949 is an apocalyptic number.

It is an amenable number.

21539949 is a deficient number, since it is larger than the sum of its proper divisors (7179987).

21539949 is an equidigital number, since it uses as much as digits as its factorization.

21539949 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7179986.

The product of its digits is 87480, while the sum is 42.

The square root of 21539949 is about 4641.1150599829. The cubic root of 21539949 is about 278.2370052433.

The spelling of 21539949 in words is "twenty-one million, five hundred thirty-nine thousand, nine hundred forty-nine".