21017853 has 8 divisors (see below), whose sum is σ = 31137600. Its totient is φ = 14011884.

The previous prime is 21017809. The next prime is 21017861. The reversal of 21017853 is 35871012.

It is not a de Polignac number, because 21017853 - 2⁹ = 21017341 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27), and also a Moran number because the ratio is a prime number: 778439 = 21017853 / (2 + 1 + 0 + 1 + 7 + 8 + 5 + 3).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21017803) 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 7 ways as a sum of consecutive naturals, for example, 389193 + ... + 389246.

It is an arithmetic number, because the mean of its divisors is an integer number (3892200).

Almost surely, 2^21017853 is an apocalyptic number.

It is an amenable number.

21017853 is a deficient number, since it is larger than the sum of its proper divisors (10119747).

21017853 is an equidigital number, since it uses as much as digits as its factorization.

21017853 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 778448 (or 778442 counting only the distinct ones).

The product of its (nonzero) digits is 1680, while the sum is 27.

The square root of 21017853 is about 4584.5232031259. The cubic root of 21017853 is about 275.9705781492.

Adding to 21017853 its reverse (35871012), we get a palindrome (56888865).

The spelling of 21017853 in words is "twenty-one million, seventeen thousand, eight hundred fifty-three".