21551213 has 4 divisors (see below), whose sum is σ = 22052448. Its totient is φ = 21049980.

The previous prime is 21551177. The next prime is 21551221. The reversal of 21551213 is 31215512.

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 21551213 - 2¹⁴ = 21534829 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21551273) 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, 250553 + ... + 250638.

It is an arithmetic number, because the mean of its divisors is an integer number (5513112).

Almost surely, 2^21551213 is an apocalyptic number.

It is an amenable number.

21551213 is a deficient number, since it is larger than the sum of its proper divisors (501235).

21551213 is an equidigital number, since it uses as much as digits as its factorization.

21551213 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 501234.

The product of its digits is 300, while the sum is 20.

The square root of 21551213 is about 4642.3284028599. The cubic root of 21551213 is about 278.2854967769.

Adding to 21551213 its reverse (31215512), we get a palindrome (52766725).

The spelling of 21551213 in words is "twenty-one million, five hundred fifty-one thousand, two hundred thirteen".