21718917 has 24 divisors (see below), whose sum is σ = 34669440. Its totient is φ = 12991680.

The previous prime is 21718897. The next prime is 21718943. The reversal of 21718917 is 71981712.

21718917 is nontrivially palindromic in base 4.

It is not a de Polignac number, because 21718917 - 2⁷ = 21718789 is a prime.

It is a super-2 number, since 2×21718917² = 943422711305778, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21718997) 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 23 ways as a sum of consecutive naturals, for example, 6433 + ... + 9209.

It is an arithmetic number, because the mean of its divisors is an integer number (1444560).

Almost surely, 2^21718917 is an apocalyptic number.

It is an amenable number.

21718917 is a deficient number, since it is larger than the sum of its proper divisors (12950523).

21718917 is a wasteful number, since it uses less digits than its factorization.

21718917 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2873 (or 2870 counting only the distinct ones).

The product of its digits is 7056, while the sum is 36.

The square root of 21718917 is about 4660.3558876978. The cubic root of 21718917 is about 279.0054725870.

The spelling of 21718917 in words is "twenty-one million, seven hundred eighteen thousand, nine hundred seventeen".