665661121 has 2 divisors, whose sum is σ = 665661122. Its totient is φ = 665661120.

The previous prime is 665661107. The next prime is 665661149. The reversal of 665661121 is 121166566.

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., 662290225 + 3370896 = 25735^2 + 1836^2 .

It is a cyclic number.

It is not a de Polignac number, because 665661121 - 2⁵ = 665661089 is a prime.

It is not a weakly prime, because it can be changed into another prime (665661221) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 332830560 + 332830561.

It is an arithmetic number, because the mean of its divisors is an integer number (332830561).

Almost surely, 2^665661121 is an apocalyptic number.

It is an amenable number.

665661121 is a deficient number, since it is larger than the sum of its proper divisors (1).

665661121 is an equidigital number, since it uses as much as digits as its factorization.

665661121 is an evil number, because the sum of its binary digits is even.

The product of its digits is 12960, while the sum is 34.

The square root of 665661121 is about 25800.4093184585. The cubic root of 665661121 is about 873.1410312015.

The spelling of 665661121 in words is "six hundred sixty-five million, six hundred sixty-one thousand, one hundred twenty-one".