21520243 has 2 divisors, whose sum is σ = 21520244. Its totient is φ = 21520242.

The previous prime is 21520241. The next prime is 21520271. The reversal of 21520243 is 34202512.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21520243 - 2¹ = 21520241 is a prime.

Together with 21520241, it forms a pair of twin primes.

It is a self number, because there is not a number n which added to its sum of digits gives 21520243.

It is not a weakly prime, because it can be changed into another prime (21520241) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10760121 + 10760122.

It is an arithmetic number, because the mean of its divisors is an integer number (10760122).

Almost surely, 2^21520243 is an apocalyptic number.

21520243 is a deficient number, since it is larger than the sum of its proper divisors (1).

21520243 is an equidigital number, since it uses as much as digits as its factorization.

21520243 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 480, while the sum is 19.

The square root of 21520243 is about 4638.9915930081. The cubic root of 21520243 is about 278.1521302155.

Adding to 21520243 its reverse (34202512), we get a palindrome (55722755).

The spelling of 21520243 in words is "twenty-one million, five hundred twenty thousand, two hundred forty-three".