21766645 has 4 divisors (see below), whose sum is σ = 26119980. Its totient is φ = 17413312.

The previous prime is 21766621. The next prime is 21766649. The reversal of 21766645 is 54666712.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 9326916 + 12439729 = 3054^2 + 3527^2 .

It is a cyclic number.

It is not a de Polignac number, because 21766645 - 2¹¹ = 21764597 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21766649) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2176660 + ... + 2176669.

It is an arithmetic number, because the mean of its divisors is an integer number (6529995).

Almost surely, 2^21766645 is an apocalyptic number.

It is an amenable number.

21766645 is a deficient number, since it is larger than the sum of its proper divisors (4353335).

21766645 is an equidigital number, since it uses as much as digits as its factorization.

21766645 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4353334.

The product of its digits is 60480, while the sum is 37.

The square root of 21766645 is about 4665.4737165694. The cubic root of 21766645 is about 279.2096974831.

The spelling of 21766645 in words is "twenty-one million, seven hundred sixty-six thousand, six hundred forty-five".