21668517 has 48 divisors (see below), whose sum is σ = 35555520. Its totient is φ = 12628224.

The previous prime is 21668501. The next prime is 21668519. The reversal of 21668517 is 71586612.

It is not a de Polignac number, because 21668517 - 2⁴ = 21668501 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21668519) by changing a digit.

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 47 ways as a sum of consecutive naturals, for example, 296793 + ... + 296865.

It is an arithmetic number, because the mean of its divisors is an integer number (740740).

Almost surely, 2^21668517 is an apocalyptic number.

It is an amenable number.

21668517 is a deficient number, since it is larger than the sum of its proper divisors (13887003).

21668517 is a wasteful number, since it uses less digits than its factorization.

21668517 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 194 (or 191 counting only the distinct ones).

The product of its digits is 20160, while the sum is 36.

The square root of 21668517 is about 4654.9454346963. The cubic root of 21668517 is about 278.7894893346.

The spelling of 21668517 in words is "twenty-one million, six hundred sixty-eight thousand, five hundred seventeen".