16666621 has 2 divisors, whose sum is σ = 16666622. Its totient is φ = 16666620.

The previous prime is 16666609. The next prime is 16666631. The reversal of 16666621 is 12666661.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13586596 + 3080025 = 3686^2 + 1755^2 .

It is a cyclic number.

It is not a de Polignac number, because 16666621 - 2⁵ = 16666589 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (16666631) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 8333310 + 8333311.

It is an arithmetic number, because the mean of its divisors is an integer number (8333311).

Almost surely, 2^16666621 is an apocalyptic number.

It is an amenable number.

16666621 is a deficient number, since it is larger than the sum of its proper divisors (1).

16666621 is an equidigital number, since it uses as much as digits as its factorization.

16666621 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 15552, while the sum is 34.

The square root of 16666621 is about 4082.4773116332. The cubic root of 16666621 is about 255.4362441657.

The spelling of 16666621 in words is "sixteen million, six hundred sixty-six thousand, six hundred twenty-one".