21718913 has 4 divisors (see below), whose sum is σ = 22224048. Its totient is φ = 21213780.

The previous prime is 21718897. The next prime is 21718943. The reversal of 21718913 is 31981712.

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 21718913 - 2⁴ = 21718897 is a prime.

It is a super-2 number, since 2×21718913² = 943422363803138, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21718913.

It is not an unprimeable number, because it can be changed into a prime (21718943) 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, 252503 + ... + 252588.

It is an arithmetic number, because the mean of its divisors is an integer number (5556012).

Almost surely, 2^21718913 is an apocalyptic number.

It is an amenable number.

21718913 is a deficient number, since it is larger than the sum of its proper divisors (505135).

21718913 is an equidigital number, since it uses as much as digits as its factorization.

21718913 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 505134.

The product of its digits is 3024, while the sum is 32.

The square root of 21718913 is about 4660.3554585461. The cubic root of 21718913 is about 279.0054554587.

The spelling of 21718913 in words is "twenty-one million, seven hundred eighteen thousand, nine hundred thirteen".