21521213 has 4 divisors (see below), whose sum is σ = 24595680. Its totient is φ = 18446748.

The previous prime is 21521183. The next prime is 21521249. The reversal of 21521213 is 31212512.

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 21521213 - 2¹⁰ = 21520189 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21521191 and 21521200.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21521263) 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, 1537223 + ... + 1537236.

It is an arithmetic number, because the mean of its divisors is an integer number (6148920).

Almost surely, 2^21521213 is an apocalyptic number.

It is an amenable number.

21521213 is a deficient number, since it is larger than the sum of its proper divisors (3074467).

21521213 is an equidigital number, since it uses as much as digits as its factorization.

21521213 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3074466.

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

The square root of 21521213 is about 4639.0961404136. The cubic root of 21521213 is about 278.1563092809.

Adding to 21521213 its reverse (31212512), we get a palindrome (52733725).

The spelling of 21521213 in words is "twenty-one million, five hundred twenty-one thousand, two hundred thirteen".