21198987 has 6 divisors (see below), whose sum is σ = 30620772. Its totient is φ = 14132652.

The previous prime is 21198979. The next prime is 21198997. The reversal of 21198987 is 78989112.

It is not a de Polignac number, because 21198987 - 2³ = 21198979 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21198907) 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, 1177713 + ... + 1177730.

It is an arithmetic number, because the mean of its divisors is an integer number (5103462).

Almost surely, 2^21198987 is an apocalyptic number.

21198987 is a deficient number, since it is larger than the sum of its proper divisors (9421785).

21198987 is a wasteful number, since it uses less digits than its factorization.

21198987 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2355449 (or 2355446 counting only the distinct ones).

The product of its digits is 72576, while the sum is 45.

The square root of 21198987 is about 4604.2357672039. The cubic root of 21198987 is about 276.7610924283.

The spelling of 21198987 in words is "twenty-one million, one hundred ninety-eight thousand, nine hundred eighty-seven".