21653639 has 18 divisors (see below), whose sum is σ = 25896240. Its totient is φ = 18052776.

The previous prime is 21653629. The next prime is 21653641. The reversal of 21653639 is 93635612.

It is not a de Polignac number, because 21653639 - 2⁴ = 21653623 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21653599 and 21653608.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21653629) 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 17 ways as a sum of consecutive naturals, for example, 90482 + ... + 90720.

It is an arithmetic number, because the mean of its divisors is an integer number (1438680).

Almost surely, 2^21653639 is an apocalyptic number.

21653639 is a deficient number, since it is larger than the sum of its proper divisors (4242601).

21653639 is an equidigital number, since it uses as much as digits as its factorization.

21653639 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 339 (or 289 counting only the distinct ones).

The product of its digits is 29160, while the sum is 35.

The square root of 21653639 is about 4653.3470749558. The cubic root of 21653639 is about 278.7256674049.

The spelling of 21653639 in words is "twenty-one million, six hundred fifty-three thousand, six hundred thirty-nine".