21761665 has 8 divisors (see below), whose sum is σ = 26472168. Its totient is φ = 17170560.

The previous prime is 21761647. The next prime is 21761681. The reversal of 21761665 is 56616712.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 5793649 + 15968016 = 2407^2 + 3996^2 .

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

It is not a de Polignac number, because 21761665 - 2⁹ = 21761153 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21761665.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 29446 + ... + 30175.

It is an arithmetic number, because the mean of its divisors is an integer number (3309021).

Almost surely, 2^21761665 is an apocalyptic number.

It is an amenable number.

21761665 is a deficient number, since it is larger than the sum of its proper divisors (4710503).

21761665 is an equidigital number, since it uses as much as digits as its factorization.

21761665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 59699.

The product of its digits is 15120, while the sum is 34.

The square root of 21761665 is about 4664.9399781776. The cubic root of 21761665 is about 279.1884023570.

The spelling of 21761665 in words is "twenty-one million, seven hundred sixty-one thousand, six hundred sixty-five".