21225557 has 4 divisors (see below), whose sum is σ = 21276396. Its totient is φ = 21174720.

The previous prime is 21225551. The next prime is 21225559. The reversal of 21225557 is 75552212.

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 2337841 + 18887716 = 1529^2 + 4346^2 .

It is a cyclic number.

It is not a de Polignac number, because 21225557 - 2⁴ = 21225541 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 (21225551) 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, 24788 + ... + 25629.

It is an arithmetic number, because the mean of its divisors is an integer number (5319099).

Almost surely, 2^21225557 is an apocalyptic number.

It is an amenable number.

21225557 is a deficient number, since it is larger than the sum of its proper divisors (50839).

21225557 is an equidigital number, since it uses as much as digits as its factorization.

21225557 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 50838.

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

The square root of 21225557 is about 4607.1202502214. The cubic root of 21225557 is about 276.8766714124.

Adding to 21225557 its reverse (75552212), we get a palindrome (96777769).

The spelling of 21225557 in words is "twenty-one million, two hundred twenty-five thousand, five hundred fifty-seven".