21215257 has 8 divisors (see below), whose sum is σ = 24290816. Its totient is φ = 18150912.

The previous prime is 21215237. The next prime is 21215261. The reversal of 21215257 is 75251212.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21215257 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21215237) 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 7 ways as a sum of consecutive naturals, for example, 1753 + ... + 6745.

It is an arithmetic number, because the mean of its divisors is an integer number (3036352).

Almost surely, 2^21215257 is an apocalyptic number.

It is an amenable number.

21215257 is a deficient number, since it is larger than the sum of its proper divisors (3075559).

21215257 is an equidigital number, since it uses as much as digits as its factorization.

21215257 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5607.

The product of its digits is 1400, while the sum is 25.

The square root of 21215257 is about 4606.0022796347. The cubic root of 21215257 is about 276.8318780667.

Adding to 21215257 its reverse (75251212), we get a palindrome (96466469).

The spelling of 21215257 in words is "twenty-one million, two hundred fifteen thousand, two hundred fifty-seven".