21909213 has 12 divisors (see below), whose sum is σ = 31943808. Its totient is φ = 14469000.

The previous prime is 21909169. The next prime is 21909227. The reversal of 21909213 is 31290912.

It is not a de Polignac number, because 21909213 - 2⁹ = 21908701 is a prime.

It is a super-2 number, since 2×21909213² = 960027228558738, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21909253) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 10413 + ... + 12338.

It is an arithmetic number, because the mean of its divisors is an integer number (2661984).

Almost surely, 2^21909213 is an apocalyptic number.

It is an amenable number.

21909213 is a deficient number, since it is larger than the sum of its proper divisors (10034595).

21909213 is a wasteful number, since it uses less digits than its factorization.

21909213 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 22864 (or 22861 counting only the distinct ones).

The product of its (nonzero) digits is 972, while the sum is 27.

The square root of 21909213 is about 4680.7278280199. The cubic root of 21909213 is about 279.8179641620.

It can be divided in two parts, 21909 and 213, that added together give a palindrome (22122).

The spelling of 21909213 in words is "twenty-one million, nine hundred nine thousand, two hundred thirteen".