21613661785 has 4 divisors (see below), whose sum is σ = 25936394148. Its totient is φ = 17290929424.

The previous prime is 21613661761. The next prime is 21613661813. The reversal of 21613661785 is 58716631612.

It is a happy number.

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 13740293961 + 7873367824 = 117219^2 + 88732^2 .

It is a cyclic number.

It is not a de Polignac number, because 21613661785 - 2¹⁵ = 21613629017 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2161366174 + ... + 2161366183.

It is an arithmetic number, because the mean of its divisors is an integer number (6484098537).

Almost surely, 2^21613661785 is an apocalyptic number.

It is an amenable number.

21613661785 is a deficient number, since it is larger than the sum of its proper divisors (4322732363).

21613661785 is an equidigital number, since it uses as much as digits as its factorization.

21613661785 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4322732362.

The product of its digits is 362880, while the sum is 46.

The spelling of 21613661785 in words is "twenty-one billion, six hundred thirteen million, six hundred sixty-one thousand, seven hundred eighty-five".