21505653 has 12 divisors (see below), whose sum is σ = 33453420. Its totient is φ = 13234176.

The previous prime is 21505643. The next prime is 21505681. The reversal of 21505653 is 35650512.

21505653 is a `hidden beast` number, since 2 + 1 + 5 + 0 + 5 + 653 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 13704804 + 7800849 = 3702^2 + 2793^2 .

It is not a de Polignac number, because 21505653 - 2⁴ = 21505637 is a prime.

It is a super-2 number, since 2×21505653² = 924986221912818, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21505643) 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, 91788 + ... + 92021.

It is an arithmetic number, because the mean of its divisors is an integer number (2787785).

Almost surely, 2^21505653 is an apocalyptic number.

It is an amenable number.

21505653 is a deficient number, since it is larger than the sum of its proper divisors (11947767).

21505653 is a wasteful number, since it uses less digits than its factorization.

21505653 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 183828 (or 183825 counting only the distinct ones).

The product of its (nonzero) digits is 4500, while the sum is 27.

The square root of 21505653 is about 4637.4187863509. The cubic root of 21505653 is about 278.0892567457.

The spelling of 21505653 in words is "twenty-one million, five hundred five thousand, six hundred fifty-three".