21765791 has 4 divisors (see below), whose sum is σ = 21801912. Its totient is φ = 21729672.

The previous prime is 21765769. The next prime is 21765839. The reversal of 21765791 is 19756712.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21765791 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21765761) 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, 17141 + ... + 18366.

It is an arithmetic number, because the mean of its divisors is an integer number (5450478).

Almost surely, 2^21765791 is an apocalyptic number.

21765791 is a deficient number, since it is larger than the sum of its proper divisors (36121).

21765791 is an equidigital number, since it uses as much as digits as its factorization.

21765791 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 36120.

The product of its digits is 26460, while the sum is 38.

The square root of 21765791 is about 4665.3821922754. The cubic root of 21765791 is about 279.2060458991.

The spelling of 21765791 in words is "twenty-one million, seven hundred sixty-five thousand, seven hundred ninety-one".