21518953 has 4 divisors (see below), whose sum is σ = 21529168. Its totient is φ = 21508740.

The previous prime is 21518947. The next prime is 21518969. The reversal of 21518953 is 35981512.

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, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21518953 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21518933) 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, 651 + ... + 6592.

It is an arithmetic number, because the mean of its divisors is an integer number (5382292).

Almost surely, 2^21518953 is an apocalyptic number.

It is an amenable number.

21518953 is a deficient number, since it is larger than the sum of its proper divisors (10215).

21518953 is an equidigital number, since it uses as much as digits as its factorization.

21518953 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10214.

The product of its digits is 10800, while the sum is 34.

The square root of 21518953 is about 4638.8525520866. The cubic root of 21518953 is about 278.1465722947.

The spelling of 21518953 in words is "twenty-one million, five hundred eighteen thousand, nine hundred fifty-three".