21661665 has 8 divisors (see below), whose sum is σ = 34658688. Its totient is φ = 11552880.

The previous prime is 21661657. The next prime is 21661681. The reversal of 21661665 is 56616612.

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

It is not a de Polignac number, because 21661665 - 2³ = 21661657 is a prime.

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, 722041 + ... + 722070.

It is an arithmetic number, because the mean of its divisors is an integer number (4332336).

Almost surely, 2^21661665 is an apocalyptic number.

It is an amenable number.

21661665 is a deficient number, since it is larger than the sum of its proper divisors (12997023).

21661665 is a wasteful number, since it uses less digits than its factorization.

21661665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1444119.

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

The square root of 21661665 is about 4654.2093850621. The cubic root of 21661665 is about 278.7601000449.

The spelling of 21661665 in words is "twenty-one million, six hundred sixty-one thousand, six hundred sixty-five".