21320243 has 6 divisors (see below), whose sum is σ = 24801156. Its totient is φ = 18274452.

The previous prime is 21320239. The next prime is 21320267. The reversal of 21320243 is 34202312.

It is not a de Polignac number, because 21320243 - 2² = 21320239 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21320203) 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 5 ways as a sum of consecutive naturals, for example, 217505 + ... + 217602.

It is an arithmetic number, because the mean of its divisors is an integer number (4133526).

Almost surely, 2^21320243 is an apocalyptic number.

21320243 is a deficient number, since it is larger than the sum of its proper divisors (3480913).

21320243 is an equidigital number, since it uses as much as digits as its factorization.

21320243 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 435121 (or 435114 counting only the distinct ones).

The product of its (nonzero) digits is 288, while the sum is 17.

The square root of 21320243 is about 4617.3848659171. The cubic root of 21320243 is about 277.2877710698.

Adding to 21320243 its reverse (34202312), we get a palindrome (55522555).

The spelling of 21320243 in words is "twenty-one million, three hundred twenty thousand, two hundred forty-three".