21549991 has 8 divisors (see below), whose sum is σ = 22560768. Its totient is φ = 20559000.

The previous prime is 21549967. The next prime is 21550003. The reversal of 21549991 is 19994512.

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 21549991 - 2¹¹ = 21547943 is a prime.

It is a super-2 number, since 2×21549991² = 928804224200162, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21549901) 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 7 ways as a sum of consecutive naturals, for example, 2695 + ... + 7096.

It is an arithmetic number, because the mean of its divisors is an integer number (2820096).

Almost surely, 2^21549991 is an apocalyptic number.

21549991 is a deficient number, since it is larger than the sum of its proper divisors (1010777).

21549991 is an equidigital number, since it uses as much as digits as its factorization.

21549991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9893.

The product of its digits is 29160, while the sum is 40.

The square root of 21549991 is about 4642.1967860055. The cubic root of 21549991 is about 278.2802368826.

The spelling of 21549991 in words is "twenty-one million, five hundred forty-nine thousand, nine hundred ninety-one".