21660017 has 4 divisors (see below), whose sum is σ = 21700596. Its totient is φ = 21619440.

The previous prime is 21660011. The next prime is 21660047. The reversal of 21660017 is 71006612.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 12845056 + 8814961 = 3584^2 + 2969^2 .

It is a cyclic number.

It is not a de Polignac number, because 21660017 - 2¹⁶ = 21594481 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21659974 and 21660001.

It is not an unprimeable number, because it can be changed into a prime (21660011) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 19478 + ... + 20559.

It is an arithmetic number, because the mean of its divisors is an integer number (5425149).

Almost surely, 2^21660017 is an apocalyptic number.

It is an amenable number.

21660017 is a deficient number, since it is larger than the sum of its proper divisors (40579).

21660017 is an equidigital number, since it uses as much as digits as its factorization.

21660017 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 40578.

The product of its (nonzero) digits is 504, while the sum is 23.

The square root of 21660017 is about 4654.0323376616. The cubic root of 21660017 is about 278.7530305930.

Adding to 21660017 its reverse (71006612), we get a palindrome (92666629).

The spelling of 21660017 in words is "twenty-one million, six hundred sixty thousand, seventeen".