21165077761 has 4 divisors (see below), whose sum is σ = 21480974512. Its totient is φ = 20849181012.

The previous prime is 21165077737. The next prime is 21165077821. The reversal of 21165077761 is 16777056112.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21165077761 - 2¹⁵ = 21165044993 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21165077701) 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, 157948275 + ... + 157948408.

It is an arithmetic number, because the mean of its divisors is an integer number (5370243628).

Almost surely, 2^21165077761 is an apocalyptic number.

It is an amenable number.

21165077761 is a deficient number, since it is larger than the sum of its proper divisors (315896751).

21165077761 is an equidigital number, since it uses as much as digits as its factorization.

21165077761 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 315896750.

The product of its (nonzero) digits is 123480, while the sum is 43.

The spelling of 21165077761 in words is "twenty-one billion, one hundred sixty-five million, seventy-seven thousand, seven hundred sixty-one".