21133391 has 4 divisors (see below), whose sum is σ = 21143232. Its totient is φ = 21123552.

The previous prime is 21133381. The next prime is 21133403. The reversal of 21133391 is 19333112.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21133391 - 2¹⁴ = 21117007 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 (21133381) 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, 170 + ... + 6503.

It is an arithmetic number, because the mean of its divisors is an integer number (5285808).

Almost surely, 2^21133391 is an apocalyptic number.

21133391 is a deficient number, since it is larger than the sum of its proper divisors (9841).

21133391 is an equidigital number, since it uses as much as digits as its factorization.

21133391 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9840.

The product of its digits is 486, while the sum is 23.

The square root of 21133391 is about 4597.1068075475. The cubic root of 21133391 is about 276.4753369825.

The spelling of 21133391 in words is "twenty-one million, one hundred thirty-three thousand, three hundred ninety-one".