21109971 has 16 divisors (see below), whose sum is σ = 30167424. Its totient is φ = 13083264.

The previous prime is 21109939. The next prime is 21109973. The reversal of 21109971 is 17990112.

It is not a de Polignac number, because 21109971 - 2⁵ = 21109939 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21109973) 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 15 ways as a sum of consecutive naturals, for example, 1740 + ... + 6726.

It is an arithmetic number, because the mean of its divisors is an integer number (1885464).

Almost surely, 2^21109971 is an apocalyptic number.

21109971 is a deficient number, since it is larger than the sum of its proper divisors (9057453).

21109971 is a wasteful number, since it uses less digits than its factorization.

21109971 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5090.

The product of its (nonzero) digits is 1134, while the sum is 30.

The square root of 21109971 is about 4594.5588471582. The cubic root of 21109971 is about 276.3731693473.

The spelling of 21109971 in words is "twenty-one million, one hundred nine thousand, nine hundred seventy-one".