21864861 has 12 divisors (see below), whose sum is σ = 31711680. Its totient is φ = 14517000.

The previous prime is 21864859. The next prime is 21864883. The reversal of 21864861 is 16846812.

21864861 is a `hidden beast` number, since 2 + 1 + 8 + 648 + 6 + 1 = 666.

It is not a de Polignac number, because 21864861 - 2¹ = 21864859 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21864061) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 2581 + ... + 7098.

It is an arithmetic number, because the mean of its divisors is an integer number (2642640).

Almost surely, 2^21864861 is an apocalyptic number.

It is an amenable number.

21864861 is a deficient number, since it is larger than the sum of its proper divisors (9846819).

21864861 is a wasteful number, since it uses less digits than its factorization.

21864861 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9936 (or 9933 counting only the distinct ones).

The product of its digits is 18432, while the sum is 36.

The square root of 21864861 is about 4675.9877031489. The cubic root of 21864861 is about 279.6290197488.

The spelling of 21864861 in words is "twenty-one million, eight hundred sixty-four thousand, eight hundred sixty-one".