21988240 has 20 divisors (see below), whose sum is σ = 51122844. Its totient is φ = 8795264.

The previous prime is 21988237. The next prime is 21988247. The reversal of 21988240 is 4288912.

It can be written as a sum of positive squares in 2 ways, for example, as 2663424 + 19324816 = 1632^2 + 4396^2 .

It is a tau number, because it is divible by the number of its divisors (20).

It is a junction number, because it is equal to n+sod(n) for n = 21988196 and 21988205.

It is not an unprimeable number, because it can be changed into a prime (21988247) 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, 137347 + ... + 137506.

Almost surely, 2^21988240 is an apocalyptic number.

21988240 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21988240 is an abundant number, since it is smaller than the sum of its proper divisors (29134604).

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

21988240 is a wasteful number, since it uses less digits than its factorization.

21988240 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 274866 (or 274860 counting only the distinct ones).

The product of its (nonzero) digits is 9216, while the sum is 34.

The square root of 21988240 is about 4689.1619720372. The cubic root of 21988240 is about 280.1539969205.

The spelling of 21988240 in words is "twenty-one million, nine hundred eighty-eight thousand, two hundred forty".