666421 has 4 divisors (see below), whose sum is σ = 761632. Its totient is φ = 571212.

The previous prime is 666403. The next prime is 666427. The reversal of 666421 is 124666.

It is a happy number.

666421 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 666421 - 2¹⁵ = 633653 is a prime.

It is a Duffinian number.

666421 is a lucky number.

It is a nialpdrome in base 10.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (666427) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 47595 + ... + 47608.

It is an arithmetic number, because the mean of its divisors is an integer number (190408).

2⁶⁶⁶⁴²¹ is an apocalyptic number.

It is an amenable number.

666421 is a deficient number, since it is larger than the sum of its proper divisors (95211).

666421 is an equidigital number, since it uses as much as digits as its factorization.

666421 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 95210.

The product of its digits is 1728, while the sum is 25.

The square root of 666421 is about 816.3461275709. The cubic root of 666421 is about 87.3473146753.

The spelling of 666421 in words is "six hundred sixty-six thousand, four hundred twenty-one".