21766643 has 4 divisors (see below), whose sum is σ = 22272888. Its totient is φ = 21260400.

The previous prime is 21766621. The next prime is 21766649. The reversal of 21766643 is 34666712.

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

It is a cyclic number.

It is not a de Polignac number, because 21766643 - 2¹⁶ = 21701107 is a prime.

It is a Duffinian 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, 253058 + ... + 253143.

It is an arithmetic number, because the mean of its divisors is an integer number (5568222).

Almost surely, 2^21766643 is an apocalyptic number.

21766643 is a deficient number, since it is larger than the sum of its proper divisors (506245).

21766643 is an equidigital number, since it uses as much as digits as its factorization.

21766643 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 506244.

The product of its digits is 36288, while the sum is 35.

The square root of 21766643 is about 4665.4735022289. The cubic root of 21766643 is about 279.2096889315.

The spelling of 21766643 in words is "twenty-one million, seven hundred sixty-six thousand, six hundred forty-three".