664391261 has 2 divisors, whose sum is σ = 664391262. Its totient is φ = 664391260.

The previous prime is 664391251. The next prime is 664391269. The reversal of 664391261 is 162193466.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 639331225 + 25060036 = 25285^2 + 5006^2 .

It is a cyclic number.

It is not a de Polignac number, because 664391261 - 2⁶ = 664391197 is a prime.

It is a super-3 number, since 3×664391261³ (a number of 27 digits) contains 333 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (664391269) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 332195630 + 332195631.

It is an arithmetic number, because the mean of its divisors is an integer number (332195631).

Almost surely, 2^664391261 is an apocalyptic number.

It is an amenable number.

664391261 is a deficient number, since it is larger than the sum of its proper divisors (1).

664391261 is an equidigital number, since it uses as much as digits as its factorization.

664391261 is an evil number, because the sum of its binary digits is even.

The product of its digits is 46656, while the sum is 38.

The square root of 664391261 is about 25775.7882711664. The cubic root of 664391261 is about 872.5854568831.

The spelling of 664391261 in words is "six hundred sixty-four million, three hundred ninety-one thousand, two hundred sixty-one".