666691523 has 2 divisors, whose sum is σ = 666691524. Its totient is φ = 666691522.

The previous prime is 666691511. The next prime is 666691579. The reversal of 666691523 is 325196666.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 666691523 - 2¹⁰ = 666690499 is a prime.

It is not a weakly prime, because it can be changed into another prime (666691583) 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, 333345761 + 333345762.

It is an arithmetic number, because the mean of its divisors is an integer number (333345762).

Almost surely, 2^666691523 is an apocalyptic number.

666691523 is a deficient number, since it is larger than the sum of its proper divisors (1).

666691523 is an equidigital number, since it uses as much as digits as its factorization.

666691523 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 349920, while the sum is 44.

The square root of 666691523 is about 25820.3703110548. The cubic root of 666691523 is about 873.5913216050.

It can be divided in two parts, 6666 and 91523, that added together give a palindrome (98189).

The spelling of 666691523 in words is "six hundred sixty-six million, six hundred ninety-one thousand, five hundred twenty-three".