21717988 has 12 divisors (see below), whose sum is σ = 40006960. Its totient is φ = 10287432.

The previous prime is 21717979. The next prime is 21717989. The reversal of 21717988 is 88971712.

It is a happy number.

It is a hoax number, since the sum of its digits (43) coincides with the sum of the digits of its distinct prime factors.

It is not an unprimeable number, because it can be changed into a prime (21717989) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 142806 + ... + 142957.

Almost surely, 2^21717988 is an apocalyptic number.

It is an amenable number.

21717988 is a deficient number, since it is larger than the sum of its proper divisors (18288972).

21717988 is a wasteful number, since it uses less digits than its factorization.

21717988 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 285786 (or 285784 counting only the distinct ones).

The product of its digits is 56448, while the sum is 43.

The square root of 21717988 is about 4660.2562161323. The cubic root of 21717988 is about 279.0014944915.

The spelling of 21717988 in words is "twenty-one million, seven hundred seventeen thousand, nine hundred eighty-eight".