21288213 has 6 divisors (see below), whose sum is σ = 30749654. Its totient is φ = 14192136.

The previous prime is 21288193. The next prime is 21288217. The reversal of 21288213 is 31288212.

It can be written as a sum of positive squares in only one way, i.e., 16990884 + 4297329 = 4122^2 + 2073^2 .

It is not a de Polignac number, because 21288213 - 2⁵ = 21288181 is a prime.

It is a Duffinian number.

It is a zygodrome in base 3.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21288217) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1182670 + ... + 1182687.

Almost surely, 2^21288213 is an apocalyptic number.

It is an amenable number.

21288213 is a deficient number, since it is larger than the sum of its proper divisors (9461441).

21288213 is a wasteful number, since it uses less digits than its factorization.

21288213 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2365363 (or 2365360 counting only the distinct ones).

The product of its digits is 1536, while the sum is 27.

The square root of 21288213 is about 4613.9151487647. The cubic root of 21288213 is about 277.1488424050.

Subtracting 21288213 from its reverse (31288212), we obtain a palindrome (9999999).

The spelling of 21288213 in words is "twenty-one million, two hundred eighty-eight thousand, two hundred thirteen".