21011305 has 32 divisors (see below), whose sum is σ = 30818304. Its totient is φ = 13438656.

The previous prime is 21011299. The next prime is 21011317. The reversal of 21011305 is 50311012.

It is not a de Polignac number, because 21011305 - 2²¹ = 18914153 is a prime.

It is a Duffinian number.

It is an unprimeable number.

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 31 ways as a sum of consecutive naturals, for example, 34312 + ... + 34918.

It is an arithmetic number, because the mean of its divisors is an integer number (963072).

Almost surely, 2^21011305 is an apocalyptic number.

It is an amenable number.

21011305 is a deficient number, since it is larger than the sum of its proper divisors (9806999).

21011305 is a wasteful number, since it uses less digits than its factorization.

21011305 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 685.

The product of its (nonzero) digits is 30, while the sum is 13.

The square root of 21011305 is about 4583.8090056197. The cubic root of 21011305 is about 275.9419161186.

Adding to 21011305 its reverse (50311012), we get a palindrome (71322317).

It can be divided in two parts, 21011 and 305, that added together give a square (21316 = 146²).

The spelling of 21011305 in words is "twenty-one million, eleven thousand, three hundred five".