21988390 has 16 divisors (see below), whose sum is σ = 39632832. Its totient is φ = 8783424.

The previous prime is 21988387. The next prime is 21988411. The reversal of 21988390 is 9388912.

21988390 is nontrivially palindromic in base 9.

It is a congruent number.

It is an unprimeable number.

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 7 ways as a sum of consecutive naturals, for example, 12442 + ... + 14098.

It is an arithmetic number, because the mean of its divisors is an integer number (2477052).

Almost surely, 2^21988390 is an apocalyptic number.

21988390 is a deficient number, since it is larger than the sum of its proper divisors (17644442).

21988390 is a wasteful number, since it uses less digits than its factorization.

21988390 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2991.

The product of its (nonzero) digits is 31104, while the sum is 40.

The square root of 21988390 is about 4689.1779663391. The cubic root of 21988390 is about 280.1546339732.

The spelling of 21988390 in words is "twenty-one million, nine hundred eighty-eight thousand, three hundred ninety".