21691863 has 24 divisors (see below), whose sum is σ = 33696000. Its totient is φ = 13403664.

The previous prime is 21691843. The next prime is 21691883. The reversal of 21691863 is 36819612.

It is an interprime number because it is at equal distance from previous prime (21691843) and next prime (21691883).

It is not a de Polignac number, because 21691863 - 2¹⁸ = 21429719 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21691843) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 6688 + ... + 9386.

It is an arithmetic number, because the mean of its divisors is an integer number (1404000).

Almost surely, 2^21691863 is an apocalyptic number.

21691863 is a deficient number, since it is larger than the sum of its proper divisors (12004137).

21691863 is a wasteful number, since it uses less digits than its factorization.

21691863 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2771 (or 2768 counting only the distinct ones).

The product of its digits is 15552, while the sum is 36.

The square root of 21691863 is about 4657.4524152159. The cubic root of 21691863 is about 278.8895774536.

The spelling of 21691863 in words is "twenty-one million, six hundred ninety-one thousand, eight hundred sixty-three".