21603 has 8 divisors (see below), whose sum is σ = 30400. Its totient is φ = 13608.

The previous prime is 21601. The next prime is 21611. The reversal of 21603 is 30612.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21603 - 2¹ = 21601 is a prime.

It is a plaindrome in base 13.

It is not an unprimeable number, because it can be changed into a prime (21601) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 133 + ... + 246.

It is an arithmetic number, because the mean of its divisors is an integer number (3800).

2²¹⁶⁰³ is an apocalyptic number.

21603 is a deficient number, since it is larger than the sum of its proper divisors (8797).

21603 is a wasteful number, since it uses less digits than its factorization.

21603 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 401.

The product of its (nonzero) digits is 36, while the sum is 12.

The square root of 21603 is about 146.9795904199. The cubic root of 21603 is about 27.8508222722.

Subtracting 21603 from its reverse (30612), we obtain a palindrome (9009).

The spelling of 21603 in words is "twenty-one thousand, six hundred three".