21620257 has 4 divisors (see below), whose sum is σ = 21633300. Its totient is φ = 21607216.

The previous prime is 21620251. The next prime is 21620267. The reversal of 21620257 is 75202612.

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 17715681 + 3904576 = 4209^2 + 1976^2 .

It is a cyclic number.

It is not a de Polignac number, because 21620257 - 2⁷ = 21620129 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21620251) 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, 3598 + ... + 7495.

It is an arithmetic number, because the mean of its divisors is an integer number (5408325).

Almost surely, 2^21620257 is an apocalyptic number.

It is an amenable number.

21620257 is a deficient number, since it is larger than the sum of its proper divisors (13043).

21620257 is a wasteful number, since it uses less digits than its factorization.

21620257 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13042.

The product of its (nonzero) digits is 1680, while the sum is 25.

The square root of 21620257 is about 4649.7588109492. The cubic root of 21620257 is about 278.5823626903.

Adding to 21620257 its reverse (75202612), we get a palindrome (96822869).

The spelling of 21620257 in words is "twenty-one million, six hundred twenty thousand, two hundred fifty-seven".