21319821 has 8 divisors (see below), whose sum is σ = 31584960. Its totient is φ = 14213196.

The previous prime is 21319817. The next prime is 21319849. The reversal of 21319821 is 12891312.

It is not a de Polignac number, because 21319821 - 2² = 21319817 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: 789623 = 21319821 / (2 + 1 + 3 + 1 + 9 + 8 + 2 + 1).

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21319421) 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, 394785 + ... + 394838.

It is an arithmetic number, because the mean of its divisors is an integer number (3948120).

Almost surely, 2^21319821 is an apocalyptic number.

It is an amenable number.

21319821 is a deficient number, since it is larger than the sum of its proper divisors (10265139).

21319821 is an equidigital number, since it uses as much as digits as its factorization.

21319821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 789632 (or 789626 counting only the distinct ones).

The product of its digits is 864, while the sum is 27.

The square root of 21319821 is about 4617.3391688287. The cubic root of 21319821 is about 277.2859415689.

The spelling of 21319821 in words is "twenty-one million, three hundred nineteen thousand, eight hundred twenty-one".