21987844 has 6 divisors (see below), whose sum is σ = 38478734. Its totient is φ = 10993920.

The previous prime is 21987841. The next prime is 21987857. The reversal of 21987844 is 44878912.

It can be written as a sum of positive squares in only one way, i.e., 17322244 + 4665600 = 4162^2 + 2160^2 .

It is a self number, because there is not a number n which added to its sum of digits gives 21987844.

It is not an unprimeable number, because it can be changed into a prime (21987841) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2748477 + ... + 2748484.

Almost surely, 2^21987844 is an apocalyptic number.

It is an amenable number.

21987844 is a deficient number, since it is larger than the sum of its proper divisors (16490890).

21987844 is a wasteful number, since it uses less digits than its factorization.

21987844 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5496965 (or 5496963 counting only the distinct ones).

The product of its digits is 129024, while the sum is 43.

The square root of 21987844 is about 4689.1197468182. The cubic root of 21987844 is about 280.1523150874.

The spelling of 21987844 in words is "twenty-one million, nine hundred eighty-seven thousand, eight hundred forty-four".