21603391 has 4 divisors (see below), whose sum is σ = 21626352. Its totient is φ = 21580432.

The previous prime is 21603389. The next prime is 21603397. The reversal of 21603391 is 19330612.

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 21603391 - 2¹ = 21603389 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21603397) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 10006 + ... + 11971.

It is an arithmetic number, because the mean of its divisors is an integer number (5406588).

Almost surely, 2^21603391 is an apocalyptic number.

21603391 is a deficient number, since it is larger than the sum of its proper divisors (22961).

21603391 is an equidigital number, since it uses as much as digits as its factorization.

21603391 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 22960.

The product of its (nonzero) digits is 972, while the sum is 25.

The square root of 21603391 is about 4647.9448146466. The cubic root of 21603391 is about 278.5099029836.

The spelling of 21603391 in words is "twenty-one million, six hundred three thousand, three hundred ninety-one".