21155072761 has 4 divisors (see below), whose sum is σ = 21196635300. Its totient is φ = 21113510224.

The previous prime is 21155072753. The next prime is 21155072797. The reversal of 21155072761 is 16727055112.

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 14875461225 + 6279611536 = 121965^2 + 79244^2 .

It is a cyclic number.

It is not a de Polignac number, because 21155072761 - 2³ = 21155072753 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21155072761.

It is not an unprimeable number, because it can be changed into a prime (21155072711) 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, 20780506 + ... + 20781523.

It is an arithmetic number, because the mean of its divisors is an integer number (5299158825).

Almost surely, 2^21155072761 is an apocalyptic number.

It is an amenable number.

21155072761 is a deficient number, since it is larger than the sum of its proper divisors (41562539).

21155072761 is an equidigital number, since it uses as much as digits as its factorization.

21155072761 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 41562538.

The product of its (nonzero) digits is 29400, while the sum is 37.

The spelling of 21155072761 in words is "twenty-one billion, one hundred fifty-five million, seventy-two thousand, seven hundred sixty-one".