21666855 has 16 divisors (see below), whose sum is σ = 39619584. Its totient is φ = 9904800.

The previous prime is 21666829. The next prime is 21666863. The reversal of 21666855 is 55866612.

It is not a de Polignac number, because 21666855 - 2⁶ = 21666791 is a prime.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 103071 + ... + 103280.

It is an arithmetic number, because the mean of its divisors is an integer number (2476224).

Almost surely, 2^21666855 is an apocalyptic number.

21666855 is a deficient number, since it is larger than the sum of its proper divisors (17952729).

21666855 is a wasteful number, since it uses less digits than its factorization.

21666855 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 206366.

The product of its digits is 86400, while the sum is 39.

The square root of 21666855 is about 4654.7669114575. The cubic root of 21666855 is about 278.7823613283.

The spelling of 21666855 in words is "twenty-one million, six hundred sixty-six thousand, eight hundred fifty-five".