21768557 has 4 divisors (see below), whose sum is σ = 22715040. Its totient is φ = 20822076.

The previous prime is 21768553. The next prime is 21768559. The reversal of 21768557 is 75586712.

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 21768557 - 2² = 21768553 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21768553) 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, 473207 + ... + 473252.

It is an arithmetic number, because the mean of its divisors is an integer number (5678760).

Almost surely, 2^21768557 is an apocalyptic number.

It is an amenable number.

21768557 is a deficient number, since it is larger than the sum of its proper divisors (946483).

21768557 is an equidigital number, since it uses as much as digits as its factorization.

21768557 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 946482.

The product of its digits is 117600, while the sum is 41.

The square root of 21768557 is about 4665.6786215941. The cubic root of 21768557 is about 279.2178725802.

The spelling of 21768557 in words is "twenty-one million, seven hundred sixty-eight thousand, five hundred fifty-seven".