21110521 has 4 divisors (see below), whose sum is σ = 21838500. Its totient is φ = 20382544.

The previous prime is 21110513. The next prime is 21110543. The reversal of 21110521 is 12501112.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 15912121 + 5198400 = 3989^2 + 2280^2 .

It is a cyclic number.

It is not a de Polignac number, because 21110521 - 2³ = 21110513 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21110591) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 363946 + ... + 364003.

It is an arithmetic number, because the mean of its divisors is an integer number (5459625).

Almost surely, 2^21110521 is an apocalyptic number.

It is an amenable number.

21110521 is a deficient number, since it is larger than the sum of its proper divisors (727979).

21110521 is an equidigital number, since it uses as much as digits as its factorization.

21110521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 727978.

The product of its (nonzero) digits is 20, while the sum is 13.

The square root of 21110521 is about 4594.6187001752. The cubic root of 21110521 is about 276.3755695388.

Adding to 21110521 its reverse (12501112), we get a palindrome (33611633).

The spelling of 21110521 in words is "twenty-one million, one hundred ten thousand, five hundred twenty-one".