21851369717 has 4 divisors (see below), whose sum is σ = 22384329996. Its totient is φ = 21318409440.

The previous prime is 21851369699. The next prime is 21851369759. The reversal of 21851369717 is 71796315812.

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 11617821796 + 10233547921 = 107786^2 + 101161^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21851369717 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21851369117) 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, 266480078 + ... + 266480159.

It is an arithmetic number, because the mean of its divisors is an integer number (5596082499).

Almost surely, 2^21851369717 is an apocalyptic number.

It is an amenable number.

21851369717 is a deficient number, since it is larger than the sum of its proper divisors (532960279).

21851369717 is an equidigital number, since it uses as much as digits as its factorization.

21851369717 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 532960278.

The product of its digits is 635040, while the sum is 50.

The spelling of 21851369717 in words is "twenty-one billion, eight hundred fifty-one million, three hundred sixty-nine thousand, seven hundred seventeen".