21521757 has 4 divisors (see below), whose sum is σ = 28695680. Its totient is φ = 14347836.

The previous prime is 21521743. The next prime is 21521771. The reversal of 21521757 is 75712512.

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 an interprime number because it is at equal distance from previous prime (21521743) and next prime (21521771).

It is not a de Polignac number, because 21521757 - 2⁶ = 21521693 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 (21521257) 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, 3586957 + ... + 3586962.

It is an arithmetic number, because the mean of its divisors is an integer number (7173920).

Almost surely, 2^21521757 is an apocalyptic number.

It is an amenable number.

21521757 is a deficient number, since it is larger than the sum of its proper divisors (7173923).

21521757 is an equidigital number, since it uses as much as digits as its factorization.

21521757 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7173922.

The product of its digits is 4900, while the sum is 30.

The square root of 21521757 is about 4639.1547721541. The cubic root of 21521757 is about 278.1586529493.

The spelling of 21521757 in words is "twenty-one million, five hundred twenty-one thousand, seven hundred fifty-seven".