21609145 has 4 divisors (see below), whose sum is σ = 25930980. Its totient is φ = 17287312.

The previous prime is 21609131. The next prime is 21609149. The reversal of 21609145 is 54190612.

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 2782224 + 18826921 = 1668^2 + 4339^2 .

It is a cyclic number.

It is not a de Polignac number, because 21609145 - 2⁷ = 21609017 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21609149) 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, 2160910 + ... + 2160919.

It is an arithmetic number, because the mean of its divisors is an integer number (6482745).

Almost surely, 2^21609145 is an apocalyptic number.

It is an amenable number.

21609145 is a deficient number, since it is larger than the sum of its proper divisors (4321835).

21609145 is an equidigital number, since it uses as much as digits as its factorization.

21609145 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4321834.

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

The square root of 21609145 is about 4648.5637566887. The cubic root of 21609145 is about 278.5346275546.

Adding to 21609145 its reverse (54190612), we get a palindrome (75799757).

The spelling of 21609145 in words is "twenty-one million, six hundred nine thousand, one hundred forty-five".