21716557 has 4 divisors (see below), whose sum is σ = 22022496. Its totient is φ = 21410620.

The previous prime is 21716533. The next prime is 21716567. The reversal of 21716557 is 75561712.

It is a happy number.

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 a de Polignac number, because none of the positive numbers 2^k-21716557 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21716507) 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, 152863 + ... + 153004.

It is an arithmetic number, because the mean of its divisors is an integer number (5505624).

Almost surely, 2^21716557 is an apocalyptic number.

It is an amenable number.

21716557 is a deficient number, since it is larger than the sum of its proper divisors (305939).

21716557 is an equidigital number, since it uses as much as digits as its factorization.

21716557 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 305938.

The product of its digits is 14700, while the sum is 34.

The square root of 21716557 is about 4660.1026812722. The cubic root of 21716557 is about 278.9953665465.

The spelling of 21716557 in words is "twenty-one million, seven hundred sixteen thousand, five hundred fifty-seven".