21005855 has 12 divisors (see below), whose sum is σ = 27296280. Its totient is φ = 15511392.

The previous prime is 21005837. The next prime is 21005857. The reversal of 21005855 is 55850012.

It is not a de Polignac number, because 21005855 - 2⁶ = 21005791 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21005857) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 11585 + ... + 13274.

It is an arithmetic number, because the mean of its divisors is an integer number (2274690).

Almost surely, 2^21005855 is an apocalyptic number.

21005855 is a deficient number, since it is larger than the sum of its proper divisors (6290425).

21005855 is a wasteful number, since it uses less digits than its factorization.

21005855 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 24890 (or 24877 counting only the distinct ones).

The product of its (nonzero) digits is 2000, while the sum is 26.

The square root of 21005855 is about 4583.2144833075. The cubic root of 21005855 is about 275.9180557334.

Adding to 21005855 its reverse (55850012), we get a palindrome (76855867).

The spelling of 21005855 in words is "twenty-one million, five thousand, eight hundred fifty-five".