21987798 has 16 divisors (see below), whose sum is σ = 50257920. Its totient is φ = 6282216.

The previous prime is 21987787. The next prime is 21987799. The reversal of 21987798 is 89778912.

It is a self number, because there is not a number n which added to its sum of digits gives 21987798.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21987799) 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, 261718 + ... + 261801.

It is an arithmetic number, because the mean of its divisors is an integer number (3141120).

Almost surely, 2^21987798 is an apocalyptic number.

21987798 is an abundant number, since it is smaller than the sum of its proper divisors (28270122).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21987798 is a wasteful number, since it uses less digits than its factorization.

21987798 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 523531.

The product of its digits is 508032, while the sum is 51.

The square root of 21987798 is about 4689.1148418438. The cubic root of 21987798 is about 280.1521197217.

The spelling of 21987798 in words is "twenty-one million, nine hundred eighty-seven thousand, seven hundred ninety-eight".