21215213 has 4 divisors (see below), whose sum is σ = 21483840. Its totient is φ = 20946588.

The previous prime is 21215203. The next prime is 21215221. The reversal of 21215213 is 31251212.

It is a happy number.

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 21215213 - 2⁸ = 21214957 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21215191 and 21215200.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21215203) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 134195 + ... + 134352.

It is an arithmetic number, because the mean of its divisors is an integer number (5370960).

Almost surely, 2^21215213 is an apocalyptic number.

It is an amenable number.

21215213 is a deficient number, since it is larger than the sum of its proper divisors (268627).

21215213 is an equidigital number, since it uses as much as digits as its factorization.

21215213 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 268626.

The product of its digits is 120, while the sum is 17.

The square root of 21215213 is about 4605.9975032559. The cubic root of 21215213 is about 276.8316866854.

Adding to 21215213 its reverse (31251212), we get a palindrome (52466425).

The spelling of 21215213 in words is "twenty-one million, two hundred fifteen thousand, two hundred thirteen".