21561213 has 8 divisors (see below), whose sum is σ = 29675776. Its totient is φ = 13910400.

The previous prime is 21561193. The next prime is 21561223. The reversal of 21561213 is 31216512.

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

It is not a de Polignac number, because 21561213 - 2⁹ = 21560701 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21561213.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21561223) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 115828 + ... + 116013.

It is an arithmetic number, because the mean of its divisors is an integer number (3709472).

Almost surely, 2^21561213 is an apocalyptic number.

It is an amenable number.

21561213 is a deficient number, since it is larger than the sum of its proper divisors (8114563).

21561213 is a wasteful number, since it uses less digits than its factorization.

21561213 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 231875.

The product of its digits is 360, while the sum is 21.

The square root of 21561213 is about 4643.4053236822. The cubic root of 21561213 is about 278.3285326322.

Adding to 21561213 its reverse (31216512), we get a palindrome (52777725).

The spelling of 21561213 in words is "twenty-one million, five hundred sixty-one thousand, two hundred thirteen".