21145609 has 4 divisors (see below), whose sum is σ = 21191940. Its totient is φ = 21099280.

The previous prime is 21145601. The next prime is 21145639. The reversal of 21145609 is 90654112.

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 10725625 + 10419984 = 3275^2 + 3228^2 .

It is a cyclic number.

It is not a de Polignac number, because 21145609 - 2³ = 21145601 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21145601) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 22474 + ... + 23395.

It is an arithmetic number, because the mean of its divisors is an integer number (5297985).

Almost surely, 2^21145609 is an apocalyptic number.

It is an amenable number.

21145609 is a deficient number, since it is larger than the sum of its proper divisors (46331).

21145609 is an equidigital number, since it uses as much as digits as its factorization.

21145609 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 46330.

The product of its (nonzero) digits is 2160, while the sum is 28.

The square root of 21145609 is about 4598.4354948178. The cubic root of 21145609 is about 276.5286069459.

The spelling of 21145609 in words is "twenty-one million, one hundred forty-five thousand, six hundred nine".