21605745 has 32 divisors (see below), whose sum is σ = 39801600. Its totient is φ = 9803520.

The previous prime is 21605711. The next prime is 21605747. The reversal of 21605745 is 54750612.

It is not a de Polignac number, because 21605745 - 2¹⁰ = 21604721 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21605747) 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 31 ways as a sum of consecutive naturals, for example, 14955 + ... + 16335.

It is an arithmetic number, because the mean of its divisors is an integer number (1243800).

Almost surely, 2^21605745 is an apocalyptic number.

It is an amenable number.

21605745 is a deficient number, since it is larger than the sum of its proper divisors (18195855).

21605745 is a wasteful number, since it uses less digits than its factorization.

21605745 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1545.

The product of its (nonzero) digits is 8400, while the sum is 30.

The square root of 21605745 is about 4648.1980379498. The cubic root of 21605745 is about 278.5200185020.

The spelling of 21605745 in words is "twenty-one million, six hundred five thousand, seven hundred forty-five".