21666671 has 8 divisors (see below), whose sum is σ = 23830464. Its totient is φ = 19573920.

The previous prime is 21666649. The next prime is 21666677. The reversal of 21666671 is 17666612.

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

It is a cyclic number.

It is not a de Polignac number, because 21666671 - 2¹⁰ = 21665647 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21666677) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 17120 + ... + 18341.

It is an arithmetic number, because the mean of its divisors is an integer number (2978808).

Almost surely, 2^21666671 is an apocalyptic number.

21666671 is a deficient number, since it is larger than the sum of its proper divisors (2163793).

21666671 is a wasteful number, since it uses less digits than its factorization.

21666671 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 35521.

The product of its digits is 18144, while the sum is 35.

The square root of 21666671 is about 4654.7471467310. The cubic root of 21666671 is about 278.7815721644.

The spelling of 21666671 in words is "twenty-one million, six hundred sixty-six thousand, six hundred seventy-one".