666644401 has 2 divisors, whose sum is σ = 666644402. Its totient is φ = 666644400.

The previous prime is 666644399. The next prime is 666644411. The reversal of 666644401 is 104446666.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 650250000 + 16394401 = 25500^2 + 4049^2 .

It is a cyclic number.

It is not a de Polignac number, because 666644401 - 2¹ = 666644399 is a prime.

Together with 666644399, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (666644411) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 333322200 + 333322201.

It is an arithmetic number, because the mean of its divisors is an integer number (333322201).

Almost surely, 2^666644401 is an apocalyptic number.

It is an amenable number.

666644401 is a deficient number, since it is larger than the sum of its proper divisors (1).

666644401 is an equidigital number, since it uses as much as digits as its factorization.

666644401 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 82944, while the sum is 37.

The square root of 666644401 is about 25819.4577983350. The cubic root of 666644401 is about 873.5707392023.

The spelling of 666644401 in words is "six hundred sixty-six million, six hundred forty-four thousand, four hundred one".