21252557 has 4 divisors (see below), whose sum is σ = 21360636. Its totient is φ = 21144480.

The previous prime is 21252551. The next prime is 21252571. The reversal of 21252557 is 75525212.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 14523721 + 6728836 = 3811^2 + 2594^2 .

It is a cyclic number.

It is not a de Polignac number, because 21252557 - 2¹⁰ = 21251533 is a prime.

It is a super-3 number, since 3×21252557³ (a number of 23 digits) contains 333 as substring.

It is a Duffinian number.

It is a plaindrome in base 16.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21252551) 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, 53744 + ... + 54137.

It is an arithmetic number, because the mean of its divisors is an integer number (5340159).

Almost surely, 2^21252557 is an apocalyptic number.

It is an amenable number.

21252557 is a deficient number, since it is larger than the sum of its proper divisors (108079).

21252557 is a wasteful number, since it uses less digits than its factorization.

21252557 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 108078.

The product of its digits is 7000, while the sum is 29.

The square root of 21252557 is about 4610.0495658941. The cubic root of 21252557 is about 276.9940221225.

Adding to 21252557 its reverse (75525212), we get a palindrome (96777769).

The spelling of 21252557 in words is "twenty-one million, two hundred fifty-two thousand, five hundred fifty-seven".