21216843 has 8 divisors (see below), whose sum is σ = 31432400. Its totient is φ = 14144544.

The previous prime is 21216841. The next prime is 21216847. The reversal of 21216843 is 34861212.

It is not a de Polignac number, because 21216843 - 2¹ = 21216841 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27), and also a Moran number because the ratio is a prime number: 785809 = 21216843 / (2 + 1 + 2 + 1 + 6 + 8 + 4 + 3).

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21216841) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 392878 + ... + 392931.

It is an arithmetic number, because the mean of its divisors is an integer number (3929050).

Almost surely, 2^21216843 is an apocalyptic number.

21216843 is a deficient number, since it is larger than the sum of its proper divisors (10215557).

21216843 is an equidigital number, since it uses as much as digits as its factorization.

21216843 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 785818 (or 785812 counting only the distinct ones).

The product of its digits is 2304, while the sum is 27.

The square root of 21216843 is about 4606.1744430710. The cubic root of 21216843 is about 276.8387763164.

The spelling of 21216843 in words is "twenty-one million, two hundred sixteen thousand, eight hundred forty-three".