21101665 has 8 divisors (see below), whose sum is σ = 27269928. Its totient is φ = 15582720.

The previous prime is 21101651. The next prime is 21101677. The reversal of 21101665 is 56610112.

It can be written as a sum of positive squares in 4 ways, for example, as 589824 + 20511841 = 768^2 + 4529^2 .

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

It is not a de Polignac number, because 21101665 - 2¹⁹ = 20577377 is a prime.

It is a Duffinian number.

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, 162256 + ... + 162385.

It is an arithmetic number, because the mean of its divisors is an integer number (3408741).

Almost surely, 2^21101665 is an apocalyptic number.

It is an amenable number.

21101665 is a deficient number, since it is larger than the sum of its proper divisors (6168263).

21101665 is a wasteful number, since it uses less digits than its factorization.

21101665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 324659.

The product of its (nonzero) digits is 360, while the sum is 22.

The square root of 21101665 is about 4593.6548629604. The cubic root of 21101665 is about 276.3369170208.

Adding to 21101665 its reverse (56610112), we get a palindrome (77711777).

The spelling of 21101665 in words is "twenty-one million, one hundred one thousand, six hundred sixty-five".