21181291 has 4 divisors (see below), whose sum is σ = 21580992. Its totient is φ = 20781592.

The previous prime is 21181289. The next prime is 21181301. The reversal of 21181291 is 19218112.

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 21181291 - 2¹ = 21181289 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21181891) 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, 199771 + ... + 199876.

It is an arithmetic number, because the mean of its divisors is an integer number (5395248).

Almost surely, 2^21181291 is an apocalyptic number.

21181291 is a deficient number, since it is larger than the sum of its proper divisors (399701).

21181291 is an equidigital number, since it uses as much as digits as its factorization.

21181291 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 399700.

The product of its digits is 288, while the sum is 25.

The square root of 21181291 is about 4602.3136572815. The cubic root of 21181291 is about 276.6840615827.

The spelling of 21181291 in words is "twenty-one million, one hundred eighty-one thousand, two hundred ninety-one".