21766521 has 16 divisors (see below), whose sum is σ = 33251328. Its totient is φ = 12406800.

The previous prime is 21766513. The next prime is 21766543. The reversal of 21766521 is 12566712.

It is not a de Polignac number, because 21766521 - 2³ = 21766513 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21766321) 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 15 ways as a sum of consecutive naturals, for example, 9256 + ... + 11366.

It is an arithmetic number, because the mean of its divisors is an integer number (2078208).

Almost surely, 2^21766521 is an apocalyptic number.

21766521 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21766521 is a deficient number, since it is larger than the sum of its proper divisors (11484807).

21766521 is a wasteful number, since it uses less digits than its factorization.

21766521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2612.

The product of its digits is 5040, while the sum is 30.

The square root of 21766521 is about 4665.4604274391. The cubic root of 21766521 is about 279.2091672825.

The spelling of 21766521 in words is "twenty-one million, seven hundred sixty-six thousand, five hundred twenty-one".