21640213 has 10 divisors (see below), whose sum is σ = 25248214. Its totient is φ = 18546696.

The previous prime is 21640189. The next prime is 21640219. The reversal of 21640213 is 31204612.

It can be written as a sum of positive squares in only one way, i.e., 18173169 + 3467044 = 4263^2 + 1862^2 .

It is not a de Polignac number, because 21640213 - 2⁵ = 21640181 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21640219) by changing a digit.

It is a polite number, since it can be written in 9 ways as a sum of consecutive naturals, for example, 2106 + ... + 6907.

Almost surely, 2^21640213 is an apocalyptic number.

It is an amenable number.

21640213 is a deficient number, since it is larger than the sum of its proper divisors (3608001).

21640213 is an frugal number, since it uses more digits than its factorization.

21640213 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9041 (or 9020 counting only the distinct ones).

The product of its (nonzero) digits is 288, while the sum is 19.

The square root of 21640213 is about 4651.9042337520. The cubic root of 21640213 is about 278.6680489987.

Adding to 21640213 its reverse (31204612), we get a palindrome (52844825).

The spelling of 21640213 in words is "twenty-one million, six hundred forty thousand, two hundred thirteen".