21511391 has 8 divisors (see below), whose sum is σ = 23520000. Its totient is φ = 19511640.

The previous prime is 21511381. The next prime is 21511397. The reversal of 21511391 is 19311512.

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

It is a cyclic number.

It is not a de Polignac number, because 21511391 - 2⁶ = 21511327 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 (21511397) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 3530 + ... + 7448.

It is an arithmetic number, because the mean of its divisors is an integer number (2940000).

Almost surely, 2^21511391 is an apocalyptic number.

21511391 is a deficient number, since it is larger than the sum of its proper divisors (2008609).

21511391 is a wasteful number, since it uses less digits than its factorization.

21511391 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4429.

The product of its digits is 270, while the sum is 23.

The square root of 21511391 is about 4638.0374082148. The cubic root of 21511391 is about 278.1139872086.

The spelling of 21511391 in words is "twenty-one million, five hundred eleven thousand, three hundred ninety-one".