1665808181 has 2 divisors, whose sum is σ = 1665808182. Its totient is φ = 1665808180.

The previous prime is 1665808171. The next prime is 1665808201. The reversal of 1665808181 is 1818085661.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1017291025 + 648517156 = 31895^2 + 25466^2 .

It is a cyclic number.

It is not a de Polignac number, because 1665808181 - 2²⁶ = 1598699317 is a prime.

It is a super-2 number, since 2×1665808181² = 5549833791773057522, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1665808171) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 832904090 + 832904091.

It is an arithmetic number, because the mean of its divisors is an integer number (832904091).

Almost surely, 2^1665808181 is an apocalyptic number.

It is an amenable number.

1665808181 is a deficient number, since it is larger than the sum of its proper divisors (1).

1665808181 is an equidigital number, since it uses as much as digits as its factorization.

1665808181 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 92160, while the sum is 44.

The square root of 1665808181 is about 40814.3134329122. The cubic root of 1665808181 is about 1185.4274970731.

The spelling of 1665808181 in words is "one billion, six hundred sixty-five million, eight hundred eight thousand, one hundred eighty-one".