21405211 has 4 divisors (see below), whose sum is σ = 21443400. Its totient is φ = 21367024.

The previous prime is 21405187. The next prime is 21405247. The reversal of 21405211 is 11250412.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21405211 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21405511) 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, 18241 + ... + 19378.

It is an arithmetic number, because the mean of its divisors is an integer number (5360850).

Almost surely, 2^21405211 is an apocalyptic number.

21405211 is a deficient number, since it is larger than the sum of its proper divisors (38189).

21405211 is an equidigital number, since it uses as much as digits as its factorization.

21405211 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 38188.

The product of its (nonzero) digits is 80, while the sum is 16.

The square root of 21405211 is about 4626.5765961454. The cubic root of 21405211 is about 277.6556430122.

Adding to 21405211 its reverse (11250412), we get a palindrome (32655623).

The spelling of 21405211 in words is "twenty-one million, four hundred five thousand, two hundred eleven".