21509845 has 16 divisors (see below), whose sum is σ = 31235328. Its totient is φ = 13881600.

The previous prime is 21509837. The next prime is 21509849. The reversal of 21509845 is 54890512.

It is not a de Polignac number, because 21509845 - 2³ = 21509837 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 21509845.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21509849) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 17481 + ... + 18670.

It is an arithmetic number, because the mean of its divisors is an integer number (1952208).

Almost surely, 2^21509845 is an apocalyptic number.

It is an amenable number.

21509845 is a deficient number, since it is larger than the sum of its proper divisors (9725483).

21509845 is a wasteful number, since it uses less digits than its factorization.

21509845 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 36180.

The product of its (nonzero) digits is 14400, while the sum is 34.

The square root of 21509845 is about 4637.8707398978. The cubic root of 21509845 is about 278.1073244669.

The spelling of 21509845 in words is "twenty-one million, five hundred nine thousand, eight hundred forty-five".