21578643 has 12 divisors (see below), whose sum is σ = 32323928. Its totient is φ = 14385600.

The previous prime is 21578633. The next prime is 21578651. The reversal of 21578643 is 34687512.

21578643 is a `hidden beast` number, since 2 + 1 + 5 + 7 + 8 + 643 = 666.

It is not a de Polignac number, because 21578643 - 2¹⁴ = 21562259 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21578598 and 21578607.

It is not an unprimeable number, because it can be changed into a prime (21578633) 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 11 ways as a sum of consecutive naturals, for example, 44158 + ... + 44643.

Almost surely, 2^21578643 is an apocalyptic number.

21578643 is a deficient number, since it is larger than the sum of its proper divisors (10745285).

21578643 is an frugal number, since it uses more digits than its factorization.

21578643 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 88816 (or 88804 counting only the distinct ones).

The product of its digits is 40320, while the sum is 36.

The square root of 21578643 is about 4645.2817998481. The cubic root of 21578643 is about 278.4035123294.

The spelling of 21578643 in words is "twenty-one million, five hundred seventy-eight thousand, six hundred forty-three".