21508265745 has 20 divisors (see below), whose sum is σ = 38555558580. Its totient is φ = 11471074848.

The previous prime is 21508265741. The next prime is 21508265759. The reversal of 21508265745 is 54756280512.

21508265745 is a `hidden beast` number, since 2 + 1 + 50 + 8 + 26 + 574 + 5 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 16250130576 + 5258135169 = 127476^2 + 72513^2 .

It is not a de Polignac number, because 21508265745 - 2² = 21508265741 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (45).

It is a self number, because there is not a number n which added to its sum of digits gives 21508265745.

It is not an unprimeable number, because it can be changed into a prime (21508265741) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 26553010 + ... + 26553819.

It is an arithmetic number, because the mean of its divisors is an integer number (1927777929).

Almost surely, 2^21508265745 is an apocalyptic number.

It is an amenable number.

21508265745 is a deficient number, since it is larger than the sum of its proper divisors (17047292835).

21508265745 is an equidigital number, since it uses as much as digits as its factorization.

21508265745 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 53106846 (or 53106837 counting only the distinct ones).

The product of its (nonzero) digits is 672000, while the sum is 45.

The spelling of 21508265745 in words is "twenty-one billion, five hundred eight million, two hundred sixty-five thousand, seven hundred forty-five".