21747791765 has 24 divisors (see below), whose sum is σ = 30432507480. Its totient is φ = 14876241408.

The previous prime is 21747791753. The next prime is 21747791803. The reversal of 21747791765 is 56719774712.

It can be written as a sum of positive squares in 4 ways, for example, as 1670602129 + 20077189636 = 40873^2 + 141694^2 .

It is not a de Polignac number, because 21747791765 - 2¹⁶ = 21747726229 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21747791765.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 8312 + ... + 208721.

It is an arithmetic number, because the mean of its divisors is an integer number (1268021145).

Almost surely, 2^21747791765 is an apocalyptic number.

It is an amenable number.

21747791765 is a deficient number, since it is larger than the sum of its proper divisors (8684715715).

21747791765 is a wasteful number, since it uses less digits than its factorization.

21747791765 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 217461 (or 217454 counting only the distinct ones).

The product of its digits is 5186160, while the sum is 56.

The spelling of 21747791765 in words is "twenty-one billion, seven hundred forty-seven million, seven hundred ninety-one thousand, seven hundred sixty-five".