21756213 has 6 divisors (see below), whose sum is σ = 31425654. Its totient is φ = 14504136.

The previous prime is 21756211. The next prime is 21756223. The reversal of 21756213 is 31265712.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 21594609 + 161604 = 4647^2 + 402^2 .

It is not a de Polignac number, because 21756213 - 2¹ = 21756211 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21756211) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1208670 + ... + 1208687.

It is an arithmetic number, because the mean of its divisors is an integer number (5237609).

Almost surely, 2^21756213 is an apocalyptic number.

It is an amenable number.

21756213 is a deficient number, since it is larger than the sum of its proper divisors (9669441).

21756213 is a wasteful number, since it uses less digits than its factorization.

21756213 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2417363 (or 2417360 counting only the distinct ones).

The product of its digits is 2520, while the sum is 27.

The square root of 21756213 is about 4664.3555825001. The cubic root of 21756213 is about 279.1650851721.

The spelling of 21756213 in words is "twenty-one million, seven hundred fifty-six thousand, two hundred thirteen".