21765213 has 16 divisors (see below), whose sum is σ = 33117760. Its totient is φ = 14117328.

The previous prime is 21765209. The next prime is 21765221. The reversal of 21765213 is 31256712.

It is a happy number.

21765213 is a `hidden beast` number, since 2 + 1 + 7 + 652 + 1 + 3 = 666.

It is not a de Polignac number, because 21765213 - 2² = 21765209 is a prime.

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

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21765223) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 9895 + ... + 11892.

It is an arithmetic number, because the mean of its divisors is an integer number (2069860).

Almost surely, 2^21765213 is an apocalyptic number.

It is an amenable number.

21765213 is a deficient number, since it is larger than the sum of its proper divisors (11352547).

21765213 is a wasteful number, since it uses less digits than its factorization.

21765213 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 21833 (or 21827 counting only the distinct ones).

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

The square root of 21765213 is about 4665.3202462425. The cubic root of 21765213 is about 279.2035743981.

The spelling of 21765213 in words is "twenty-one million, seven hundred sixty-five thousand, two hundred thirteen".