21717818 has 8 divisors (see below), whose sum is σ = 32681748. Its totient is φ = 10823904.

The previous prime is 21717803. The next prime is 21717827. The reversal of 21717818 is 81871712.

It can be written as a sum of positive squares in 2 ways, for example, as 20097289 + 1620529 = 4483^2 + 1273^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a super-2 number, since 2×21717818² = 943327237362248, which contains 22 as substring.

It is an unprimeable number.

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, 16721 + ... + 17972.

Almost surely, 2^21717818 is an apocalyptic number.

21717818 is a deficient number, since it is larger than the sum of its proper divisors (10963930).

21717818 is a wasteful number, since it uses less digits than its factorization.

21717818 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 35008.

The product of its digits is 6272, while the sum is 35.

The square root of 21717818 is about 4660.2379767561. The cubic root of 21717818 is about 279.0007665177. Note that the first 3 decimals are identical.

The spelling of 21717818 in words is "twenty-one million, seven hundred seventeen thousand, eight hundred eighteen".