21945865 has 8 divisors (see below), whose sum is σ = 26977608. Its totient is φ = 17128320.

The previous prime is 21945863. The next prime is 21945871. The reversal of 21945865 is 56854912.

It can be written as a sum of positive squares in 4 ways, for example, as 822649 + 21123216 = 907^2 + 4596^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21945865 - 2¹ = 21945863 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21945863) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 53322 + ... + 53731.

It is an arithmetic number, because the mean of its divisors is an integer number (3372201).

Almost surely, 2^21945865 is an apocalyptic number.

It is an amenable number.

21945865 is a deficient number, since it is larger than the sum of its proper divisors (5031743).

21945865 is a wasteful number, since it uses less digits than its factorization.

21945865 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 107099.

The product of its digits is 86400, while the sum is 40.

The square root of 21945865 is about 4684.6413950269. The cubic root of 21945865 is about 279.9739133860.

The spelling of 21945865 in words is "twenty-one million, nine hundred forty-five thousand, eight hundred sixty-five".