21604145 has 4 divisors (see below), whose sum is σ = 25924980. Its totient is φ = 17283312.

The previous prime is 21604139. The next prime is 21604151. The reversal of 21604145 is 54140612.

It is a semiprime because it is the product of two primes.

It is an interprime number because it is at equal distance from previous prime (21604139) and next prime (21604151).

It can be written as a sum of positive squares in 2 ways, for example, as 5914624 + 15689521 = 2432^2 + 3961^2 .

It is a cyclic number.

It is not a de Polignac number, because 21604145 - 2⁶ = 21604081 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21604145.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2160410 + ... + 2160419.

It is an arithmetic number, because the mean of its divisors is an integer number (6481245).

Almost surely, 2^21604145 is an apocalyptic number.

It is an amenable number.

21604145 is a deficient number, since it is larger than the sum of its proper divisors (4320835).

21604145 is an equidigital number, since it uses as much as digits as its factorization.

21604145 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4320834.

The product of its (nonzero) digits is 960, while the sum is 23.

The square root of 21604145 is about 4648.0259250568. The cubic root of 21604145 is about 278.5131431234.

Adding to 21604145 its reverse (54140612), we get a palindrome (75744757).

It can be divided in two parts, 216041 and 45, that multiplied together give a triangular number (9721845 = T₄₄₀₉).

The spelling of 21604145 in words is "twenty-one million, six hundred four thousand, one hundred forty-five".