666621 has 12 divisors (see below), whose sum is σ = 1019772. Its totient is φ = 418176.

The previous prime is 666607. The next prime is 666637. The reversal of 666621 is 126666.

It can be written as a sum of positive squares in 2 ways, for example, as 622521 + 44100 = 789^2 + 210^2 .

It is not a de Polignac number, because 666621 - 2⁶ = 666557 is a prime.

It is a nialpdrome in base 10.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 666621.

It is not an unprimeable number, because it can be changed into a prime (666671) 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 11 ways as a sum of consecutive naturals, for example, 2026 + ... + 2331.

It is an arithmetic number, because the mean of its divisors is an integer number (84981).

2⁶⁶⁶⁶²¹ is an apocalyptic number.

It is an amenable number.

666621 is a deficient number, since it is larger than the sum of its proper divisors (353151).

666621 is a wasteful number, since it uses less digits than its factorization.

666621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4380 (or 4377 counting only the distinct ones).

The product of its digits is 2592, while the sum is 27.

The square root of 666621 is about 816.4686154409. The cubic root of 666621 is about 87.3560517527.

The spelling of 666621 in words is "six hundred sixty-six thousand, six hundred twenty-one".