21651213 has 4 divisors (see below), whose sum is σ = 28868288. Its totient is φ = 14434140.

The previous prime is 21651209. The next prime is 21651221. The reversal of 21651213 is 31215612.

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 not a de Polignac number, because 21651213 - 2² = 21651209 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 21651213.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21651283) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3608533 + ... + 3608538.

It is an arithmetic number, because the mean of its divisors is an integer number (7217072).

Almost surely, 2^21651213 is an apocalyptic number.

It is an amenable number.

21651213 is a deficient number, since it is larger than the sum of its proper divisors (7217075).

21651213 is an equidigital number, since it uses as much as digits as its factorization.

21651213 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7217074.

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

The square root of 21651213 is about 4653.0863950716. The cubic root of 21651213 is about 278.7152578578.

Adding to 21651213 its reverse (31215612), we get a palindrome (52866825).

The spelling of 21651213 in words is "twenty-one million, six hundred fifty-one thousand, two hundred thirteen".