16666821 has 6 divisors (see below), whose sum is σ = 24074310. Its totient is φ = 11111208.

The previous prime is 16666807. The next prime is 16666823. The reversal of 16666821 is 12866661.

It can be written as a sum of positive squares in only one way, i.e., 13793796 + 2873025 = 3714^2 + 1695^2 .

It is not a de Polignac number, because 16666821 - 2¹⁷ = 16535749 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (16666823) 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 5 ways as a sum of consecutive naturals, for example, 925926 + ... + 925943.

It is an arithmetic number, because the mean of its divisors is an integer number (4012385).

Almost surely, 2^16666821 is an apocalyptic number.

It is an amenable number.

16666821 is a deficient number, since it is larger than the sum of its proper divisors (7407489).

16666821 is a wasteful number, since it uses less digits than its factorization.

16666821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1851875 (or 1851872 counting only the distinct ones).

The product of its digits is 20736, while the sum is 36.

The square root of 16666821 is about 4082.5018064907. The cubic root of 16666821 is about 255.4372659093.

The spelling of 16666821 in words is "sixteen million, six hundred sixty-six thousand, eight hundred twenty-one".