21993988 has 12 divisors (see below), whose sum is σ = 40753692. Its totient is φ = 10350080.

The previous prime is 21993967. The next prime is 21993989. The reversal of 21993988 is 88939912.

It can be written as a sum of positive squares in 2 ways, for example, as 11957764 + 10036224 = 3458^2 + 3168^2 .

It is not an unprimeable number, because it can be changed into a prime (21993989) 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 3 ways as a sum of consecutive naturals, for example, 161653 + ... + 161788.

It is an arithmetic number, because the mean of its divisors is an integer number (3396141).

Almost surely, 2^21993988 is an apocalyptic number.

It is an amenable number.

21993988 is a deficient number, since it is larger than the sum of its proper divisors (18759704).

21993988 is a wasteful number, since it uses less digits than its factorization.

21993988 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 323462 (or 323460 counting only the distinct ones).

The product of its digits is 279936, while the sum is 49.

The square root of 21993988 is about 4689.7748346802. The cubic root of 21993988 is about 280.1784067092.

It can be divided in two parts, 21 and 993988, that added together give a square (994009 = 997²).

The spelling of 21993988 in words is "twenty-one million, nine hundred ninety-three thousand, nine hundred eighty-eight".