21166665 has 64 divisors (see below), whose sum is σ = 39916800. Its totient is φ = 9483264.

The previous prime is 21166643. The next prime is 21166679. The reversal of 21166665 is 56666112.

It is not a de Polignac number, because 21166665 - 2¹⁵ = 21133897 is a prime.

It is an unprimeable number.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 107347 + ... + 107543.

It is an arithmetic number, because the mean of its divisors is an integer number (623700).

Almost surely, 2^21166665 is an apocalyptic number.

It is an amenable number.

21166665 is a deficient number, since it is larger than the sum of its proper divisors (18750135).

21166665 is a wasteful number, since it uses less digits than its factorization.

21166665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 266.

The product of its digits is 12960, while the sum is 33.

The square root of 21166665 is about 4600.7243994832. The cubic root of 21166665 is about 276.6203620834.

The spelling of 21166665 in words is "twenty-one million, one hundred sixty-six thousand, six hundred sixty-five".