21865772017 has 4 divisors (see below), whose sum is σ = 22066375540. Its totient is φ = 21665168496.

The previous prime is 21865772009. The next prime is 21865772039. The reversal of 21865772017 is 71027756812.

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 19712440801 + 2153331216 = 140401^2 + 46404^2 .

It is a cyclic number.

It is not a de Polignac number, because 21865772017 - 2³ = 21865772009 is a prime.

It is a super-2 number, since 2×21865772017² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21865772057) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 100301598 + ... + 100301815.

It is an arithmetic number, because the mean of its divisors is an integer number (5516593885).

Almost surely, 2^21865772017 is an apocalyptic number.

It is an amenable number.

21865772017 is a deficient number, since it is larger than the sum of its proper divisors (200603523).

21865772017 is a wasteful number, since it uses less digits than its factorization.

21865772017 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 200603522.

The product of its (nonzero) digits is 329280, while the sum is 46.

The spelling of 21865772017 in words is "twenty-one billion, eight hundred sixty-five million, seven hundred seventy-two thousand, seventeen".