21673765 has 4 divisors (see below), whose sum is σ = 26008524. Its totient is φ = 17339008.

The previous prime is 21673753. The next prime is 21673787. The reversal of 21673765 is 56737612.

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 9847044 + 11826721 = 3138^2 + 3439^2 .

It is a cyclic number.

It is not a de Polignac number, because 21673765 - 2¹⁹ = 21149477 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2167372 + ... + 2167381.

It is an arithmetic number, because the mean of its divisors is an integer number (6502131).

Almost surely, 2^21673765 is an apocalyptic number.

It is an amenable number.

21673765 is a deficient number, since it is larger than the sum of its proper divisors (4334759).

21673765 is an equidigital number, since it uses as much as digits as its factorization.

21673765 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4334758.

The product of its digits is 52920, while the sum is 37.

The square root of 21673765 is about 4655.5091021284. The cubic root of 21673765 is about 278.8119946302.

The spelling of 21673765 in words is "twenty-one million, six hundred seventy-three thousand, seven hundred sixty-five".