21072557 has 4 divisors (see below), whose sum is σ = 22988256. Its totient is φ = 19156860.

The previous prime is 21072553. The next prime is 21072559. The reversal of 21072557 is 75527012.

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 21072557 - 2² = 21072553 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 (21072551) 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, 957833 + ... + 957854.

It is an arithmetic number, because the mean of its divisors is an integer number (5747064).

Almost surely, 2^21072557 is an apocalyptic number.

It is an amenable number.

21072557 is a deficient number, since it is larger than the sum of its proper divisors (1915699).

21072557 is a wasteful number, since it uses less digits than its factorization.

21072557 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1915698.

The product of its (nonzero) digits is 4900, while the sum is 29.

The square root of 21072557 is about 4590.4854863075. The cubic root of 21072557 is about 276.2097972522.

Adding to 21072557 its reverse (75527012), we get a palindrome (96599569).

It can be divided in two parts, 2107 and 2557, that added together give a palindrome (4664).

The spelling of 21072557 in words is "twenty-one million, seventy-two thousand, five hundred fifty-seven".