21571891 has 8 divisors (see below), whose sum is σ = 23675904. Its totient is φ = 19491720.

The previous prime is 21571867. The next prime is 21571903. The reversal of 21571891 is 19817512.

It is a happy number.

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 21571891 - 2⁷ = 21571763 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21571801) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 4035 + ... + 7708.

It is an arithmetic number, because the mean of its divisors is an integer number (2959488).

Almost surely, 2^21571891 is an apocalyptic number.

21571891 is a deficient number, since it is larger than the sum of its proper divisors (2104013).

21571891 is a wasteful number, since it uses less digits than its factorization.

21571891 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11921.

The product of its digits is 5040, while the sum is 34.

The square root of 21571891 is about 4644.5549840647. The cubic root of 21571891 is about 278.3744716306.

The spelling of 21571891 in words is "twenty-one million, five hundred seventy-one thousand, eight hundred ninety-one".