21809953 has 4 divisors (see below), whose sum is σ = 23792688. Its totient is φ = 19827220.

The previous prime is 21809951. The next prime is 21809971. The reversal of 21809953 is 35990812.

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 21809953 - 2¹ = 21809951 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21809951) 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 in 3 ways as a sum of consecutive naturals, for example, 991351 + ... + 991372.

It is an arithmetic number, because the mean of its divisors is an integer number (5948172).

Almost surely, 2^21809953 is an apocalyptic number.

It is an amenable number.

21809953 is a deficient number, since it is larger than the sum of its proper divisors (1982735).

21809953 is a wasteful number, since it uses less digits than its factorization.

21809953 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1982734.

The product of its (nonzero) digits is 19440, while the sum is 37.

The square root of 21809953 is about 4670.1127395385. The cubic root of 21809953 is about 279.3947513091.

The spelling of 21809953 in words is "twenty-one million, eight hundred nine thousand, nine hundred fifty-three".