21657988 has 12 divisors (see below), whose sum is σ = 41347152. Its totient is φ = 9844520.

The previous prime is 21657971. The next prime is 21657991. The reversal of 21657988 is 88975612.

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 3 ways as a sum of consecutive naturals, for example, 246070 + ... + 246157.

It is an arithmetic number, because the mean of its divisors is an integer number (3445596).

Almost surely, 2^21657988 is an apocalyptic number.

It is an amenable number.

21657988 is a deficient number, since it is larger than the sum of its proper divisors (19689164).

21657988 is a wasteful number, since it uses less digits than its factorization.

21657988 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 492242 (or 492240 counting only the distinct ones).

The product of its digits is 241920, while the sum is 46.

The square root of 21657988 is about 4653.8143495417. The cubic root of 21657988 is about 278.7443262668.

It can be divided in two parts, 2165 and 7988, that added together give a triangular number (10153 = T₁₄₂).

The spelling of 21657988 in words is "twenty-one million, six hundred fifty-seven thousand, nine hundred eighty-eight".