21331987 has 6 divisors (see below), whose sum is σ = 21633612. Its totient is φ = 21034512.

The previous prime is 21331963. The next prime is 21331993. The reversal of 21331987 is 78913312.

It is not a de Polignac number, because 21331987 - 2¹¹ = 21329939 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21331187) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 3328 + ... + 7330.

It is an arithmetic number, because the mean of its divisors is an integer number (3605602).

Almost surely, 2^21331987 is an apocalyptic number.

21331987 is a deficient number, since it is larger than the sum of its proper divisors (301625).

21331987 is an frugal number, since it uses more digits than its factorization.

21331987 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4149 (or 4076 counting only the distinct ones).

The product of its digits is 9072, while the sum is 34.

The square root of 21331987 is about 4618.6564063589. The cubic root of 21331987 is about 277.3386752713.

The spelling of 21331987 in words is "twenty-one million, three hundred thirty-one thousand, nine hundred eighty-seven".