21738213 has 30 divisors (see below), whose sum is σ = 37781766. Its totient is φ = 12419568.

The previous prime is 21738191. The next prime is 21738221. The reversal of 21738213 is 31283712.

It can be written as a sum of positive squares in only one way, i.e., 21734244 + 3969 = 4662^2 + 63^2 .

It is not a de Polignac number, because 21738213 - 2⁵ = 21738181 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21738293) by changing a digit.

It is a polite number, since it can be written in 29 ways as a sum of consecutive naturals, for example, 1231 + ... + 6707.

Almost surely, 2^21738213 is an apocalyptic number.

It is an amenable number.

21738213 is a deficient number, since it is larger than the sum of its proper divisors (16043553).

21738213 is an equidigital number, since it uses as much as digits as its factorization.

21738213 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5503 (or 5487 counting only the distinct ones).

The product of its digits is 2016, while the sum is 27.

The square root of 21738213 is about 4662.4256562438. The cubic root of 21738213 is about 279.0880748644.

The spelling of 21738213 in words is "twenty-one million, seven hundred thirty-eight thousand, two hundred thirteen".