666649 has 2 divisors, whose sum is σ = 666650. Its totient is φ = 666648.

The previous prime is 666647. The next prime is 666667. The reversal of 666649 is 946666.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 409600 + 257049 = 640^2 + 507^2 .

It is a cyclic number.

It is not a de Polignac number, because 666649 - 2¹ = 666647 is a prime.

Together with 666647, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (666643) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 333324 + 333325.

It is an arithmetic number, because the mean of its divisors is an integer number (333325).

2⁶⁶⁶⁶⁴⁹ is an apocalyptic number.

It is an amenable number.

666649 is a deficient number, since it is larger than the sum of its proper divisors (1).

666649 is an equidigital number, since it uses as much as digits as its factorization.

666649 is an evil number, because the sum of its binary digits is even.

The product of its digits is 46656, while the sum is 37.

The square root of 666649 is about 816.4857622764. The cubic root of 666649 is about 87.3572748041.

It can be divided in two parts, 666 and 649, that multiplied together give a palindrome (432234).

The spelling of 666649 in words is "six hundred sixty-six thousand, six hundred forty-nine".