21531603 has 4 divisors (see below), whose sum is σ = 28708808. Its totient is φ = 14354400.

The previous prime is 21531599. The next prime is 21531619. The reversal of 21531603 is 30613512.

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

It is not a de Polignac number, because 21531603 - 2² = 21531599 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21531603.

It is not an unprimeable number, because it can be changed into a prime (21531623) 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, 3588598 + ... + 3588603.

It is an arithmetic number, because the mean of its divisors is an integer number (7177202).

Almost surely, 2^21531603 is an apocalyptic number.

21531603 is a deficient number, since it is larger than the sum of its proper divisors (7177205).

21531603 is an equidigital number, since it uses as much as digits as its factorization.

21531603 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7177204.

The product of its (nonzero) digits is 540, while the sum is 21.

The square root of 21531603 is about 4640.2158354973. The cubic root of 21531603 is about 278.2010647987.

The spelling of 21531603 in words is "twenty-one million, five hundred thirty-one thousand, six hundred three".