21615665 has 8 divisors (see below), whose sum is σ = 26294568. Its totient is φ = 17055360.

The previous prime is 21615647. The next prime is 21615667. The reversal of 21615665 is 56651612.

It can be written as a sum of positive squares in 4 ways, for example, as 1437601 + 20178064 = 1199^2 + 4492^2 .

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

It is not a de Polignac number, because 21615665 - 2⁸ = 21615409 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21615667) by changing a digit.

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, 29246 + ... + 29975.

It is an arithmetic number, because the mean of its divisors is an integer number (3286821).

Almost surely, 2^21615665 is an apocalyptic number.

It is an amenable number.

21615665 is a deficient number, since it is larger than the sum of its proper divisors (4678903).

21615665 is an equidigital number, since it uses as much as digits as its factorization.

21615665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 59299.

The product of its digits is 10800, while the sum is 32.

The square root of 21615665 is about 4649.2649956740. The cubic root of 21615665 is about 278.5626382750.

The spelling of 21615665 in words is "twenty-one million, six hundred fifteen thousand, six hundred sixty-five".