21026665 has 8 divisors (see below), whose sum is σ = 27525888. Its totient is φ = 15292080.

The previous prime is 21026657. The next prime is 21026689. The reversal of 21026665 is 56662012.

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

It is not a de Polignac number, because 21026665 - 2³ = 21026657 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, 191097 + ... + 191206.

It is an arithmetic number, because the mean of its divisors is an integer number (3440736).

Almost surely, 2^21026665 is an apocalyptic number.

It is an amenable number.

21026665 is a deficient number, since it is larger than the sum of its proper divisors (6499223).

21026665 is a wasteful number, since it uses less digits than its factorization.

21026665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 382319.

The product of its (nonzero) digits is 4320, while the sum is 28.

The square root of 21026665 is about 4585.4841620051. The cubic root of 21026665 is about 276.0091408091.

Adding to 21026665 its reverse (56662012), we get a palindrome (77688677).

The spelling of 21026665 in words is "twenty-one million, twenty-six thousand, six hundred sixty-five".