21666785 has 16 divisors (see below), whose sum is σ = 29911296. Its totient is φ = 14758848.

The previous prime is 21666779. The next prime is 21666791. The reversal of 21666785 is 58766612.

It is an interprime number because it is at equal distance from previous prime (21666779) and next prime (21666791).

It is a cyclic number.

It is not a de Polignac number, because 21666785 - 2⁴ = 21666769 is a prime.

It is a Duffinian number.

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 15 ways as a sum of consecutive naturals, for example, 3524 + ... + 7466.

It is an arithmetic number, because the mean of its divisors is an integer number (1869456).

Almost surely, 2^21666785 is an apocalyptic number.

It is an amenable number.

21666785 is a deficient number, since it is larger than the sum of its proper divisors (8244511).

21666785 is a wasteful number, since it uses less digits than its factorization.

21666785 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4112.

The product of its digits is 120960, while the sum is 41.

The square root of 21666785 is about 4654.7593922780. The cubic root of 21666785 is about 278.7820611034.

The spelling of 21666785 in words is "twenty-one million, six hundred sixty-six thousand, seven hundred eighty-five".