21431665 has 8 divisors (see below), whose sum is σ = 25983720. Its totient is φ = 16968192.

The previous prime is 21431647. The next prime is 21431681. The reversal of 21431665 is 56613412.

It can be written as a sum of positive squares in 4 ways, for example, as 59536 + 21372129 = 244^2 + 4623^2 .

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

It is a cyclic number.

It is not a de Polignac number, because 21431665 - 2¹⁹ = 20907377 is a prime.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 21610 + ... + 22579.

It is an arithmetic number, because the mean of its divisors is an integer number (3247965).

Almost surely, 2^21431665 is an apocalyptic number.

It is an amenable number.

21431665 is a deficient number, since it is larger than the sum of its proper divisors (4552055).

21431665 is an equidigital number, since it uses as much as digits as its factorization.

21431665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 44291.

The product of its digits is 4320, while the sum is 28.

The square root of 21431665 is about 4629.4346307082. The cubic root of 21431665 is about 277.7699777662.

The spelling of 21431665 in words is "twenty-one million, four hundred thirty-one thousand, six hundred sixty-five".