21066665 has 4 divisors (see below), whose sum is σ = 25280004. Its totient is φ = 16853328.

The previous prime is 21066641. The next prime is 21066677. The reversal of 21066665 is 56666012.

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 7198489 + 13868176 = 2683^2 + 3724^2 .

It is a cyclic number.

It is not a de Polignac number, because 21066665 - 2⁶ = 21066601 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2106662 + ... + 2106671.

It is an arithmetic number, because the mean of its divisors is an integer number (6320001).

Almost surely, 2^21066665 is an apocalyptic number.

It is an amenable number.

21066665 is a deficient number, since it is larger than the sum of its proper divisors (4213339).

21066665 is an equidigital number, since it uses as much as digits as its factorization.

21066665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4213338.

The product of its (nonzero) digits is 12960, while the sum is 32.

The square root of 21066665 is about 4589.8436792553. The cubic root of 21066665 is about 276.1840516054.

The spelling of 21066665 in words is "twenty-one million, sixty-six thousand, six hundred sixty-five".