21118705 has 4 divisors (see below), whose sum is σ = 25342452. Its totient is φ = 16894960.

The previous prime is 21118663. The next prime is 21118717. The reversal of 21118705 is 50781112.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 9511056 + 11607649 = 3084^2 + 3407^2 .

It is not a de Polignac number, because 21118705 - 2¹³ = 21110513 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21118705.

It is an unprimeable number.

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 3 ways as a sum of consecutive naturals, for example, 2111866 + ... + 2111875.

It is an arithmetic number, because the mean of its divisors is an integer number (6335613).

Almost surely, 2^21118705 is an apocalyptic number.

It is an amenable number.

21118705 is a deficient number, since it is larger than the sum of its proper divisors (4223747).

21118705 is an equidigital number, since it uses as much as digits as its factorization.

21118705 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4223746.

The product of its (nonzero) digits is 560, while the sum is 25.

The square root of 21118705 is about 4595.5092209678. The cubic root of 21118705 is about 276.4112794650.

Adding to 21118705 its reverse (50781112), we get a palindrome (71899817).

It can be divided in two parts, 2111 and 8705, that added together give a square (10816 = 104²).

The spelling of 21118705 in words is "twenty-one million, one hundred eighteen thousand, seven hundred five".