21663859 has 8 divisors (see below), whose sum is σ = 24986720. Its totient is φ = 18398016.

The previous prime is 21663821. The next prime is 21663869. The reversal of 21663859 is 95836612.

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

It is not a de Polignac number, because 21663859 - 2²¹ = 19566707 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21663809) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 13434 + ... + 14959.

It is an arithmetic number, because the mean of its divisors is an integer number (3123340).

Almost surely, 2^21663859 is an apocalyptic number.

21663859 is a deficient number, since it is larger than the sum of its proper divisors (3322861).

21663859 is a wasteful number, since it uses less digits than its factorization.

21663859 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 28509.

The product of its digits is 77760, while the sum is 40.

The square root of 21663859 is about 4654.4450797061. The cubic root of 21663859 is about 278.7695111253.

It can be divided in two parts, 21663 and 859, that added together give a palindrome (22522).

The spelling of 21663859 in words is "twenty-one million, six hundred sixty-three thousand, eight hundred fifty-nine".