21634821 has 12 divisors (see below), whose sum is σ = 33654348. Its totient is φ = 13313664.

The previous prime is 21634813. The next prime is 21634849. The reversal of 21634821 is 12843612.

21634821 is a `hidden beast` number, since 2 + 1 + 634 + 8 + 21 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 2842596 + 18792225 = 1686^2 + 4335^2 .

It is not a de Polignac number, because 21634821 - 2³ = 21634813 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21634801) 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 11 ways as a sum of consecutive naturals, for example, 92340 + ... + 92573.

It is an arithmetic number, because the mean of its divisors is an integer number (2804529).

Almost surely, 2^21634821 is an apocalyptic number.

It is an amenable number.

21634821 is a deficient number, since it is larger than the sum of its proper divisors (12019527).

21634821 is a wasteful number, since it uses less digits than its factorization.

21634821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 184932 (or 184929 counting only the distinct ones).

The product of its digits is 2304, while the sum is 27.

The square root of 21634821 is about 4651.3246500325. The cubic root of 21634821 is about 278.6449022312.

The spelling of 21634821 in words is "twenty-one million, six hundred thirty-four thousand, eight hundred twenty-one".