21653603 has 4 divisors (see below), whose sum is σ = 22595088. Its totient is φ = 20712120.

The previous prime is 21653581. The next prime is 21653623. The reversal of 21653603 is 30635612.

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

It is a cyclic number.

It is not a de Polignac number, because 21653603 - 2⁶ = 21653539 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21653623) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 470708 + ... + 470753.

It is an arithmetic number, because the mean of its divisors is an integer number (5648772).

Almost surely, 2^21653603 is an apocalyptic number.

21653603 is a gapful number since it is divisible by the number (23) formed by its first and last digit.

21653603 is a deficient number, since it is larger than the sum of its proper divisors (941485).

21653603 is an equidigital number, since it uses as much as digits as its factorization.

21653603 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 941484.

The product of its (nonzero) digits is 3240, while the sum is 26.

The square root of 21653603 is about 4653.3432067708. The cubic root of 21653603 is about 278.7255129408.

Subtracting 21653603 from its reverse (30635612), we obtain a square (8982009 = 2997²).

The spelling of 21653603 in words is "twenty-one million, six hundred fifty-three thousand, six hundred three".