21128291 has 8 divisors (see below), whose sum is σ = 21745584. Its totient is φ = 20519200.

The previous prime is 21128281. The next prime is 21128293. The reversal of 21128291 is 19282112.

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 21128291 - 2¹⁸ = 20866147 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 21128291.

It is not an unprimeable number, because it can be changed into a prime (21128293) 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, 3380 + ... + 7326.

It is an arithmetic number, because the mean of its divisors is an integer number (2718198).

Almost surely, 2^21128291 is an apocalyptic number.

21128291 is a deficient number, since it is larger than the sum of its proper divisors (617293).

21128291 is a wasteful number, since it uses less digits than its factorization.

21128291 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4101.

The product of its digits is 576, while the sum is 26.

The square root of 21128291 is about 4596.5520773728. The cubic root of 21128291 is about 276.4530951243.

The spelling of 21128291 in words is "twenty-one million, one hundred twenty-eight thousand, two hundred ninety-one".