21205523 has 2 divisors, whose sum is σ = 21205524.
Its totient is φ = 21205522.
The previous prime is 21205453. The next prime is 21205529. The reversal of 21205523 is 32550212.
It is a strong prime.
It is a cyclic number.
It is not a de Polignac number, because 21205523 - 210 = 21204499 is a prime.
It is a junction number, because it is equal to n+sod(n) for n = 21205495 and 21205504.
It is not a weakly prime, because it can be changed into another prime (21205529) by changing a digit.
It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10602761 + 10602762.
It is an arithmetic number, because the mean of its divisors is an integer number (10602762).
Almost surely, 221205523 is an apocalyptic number.
21205523 is a deficient number, since it is larger than the sum of its proper divisors (1).
21205523 is an equidigital number, since it uses as much as digits as its factorization.
21205523 is an evil number, because the sum of its binary digits is even.
The product of its (nonzero) digits is 600, while the sum is 20.
The square root of 21205523 is about 4604.9454937057.
The cubic root of 21205523 is about 276.7895328537.
Adding to 21205523 its reverse (32550212), we get a palindrome (53755735).
The spelling of 21205523 in words is "twenty-one million, two hundred five thousand, five hundred twenty-three".