165731981 has 2 divisors, whose sum is σ = 165731982. Its totient is φ = 165731980.

The previous prime is 165731977. The next prime is 165731987. The reversal of 165731981 is 189137561.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 165533956 + 198025 = 12866^2 + 445^2 .

It is a cyclic number.

It is not a de Polignac number, because 165731981 - 2² = 165731977 is a prime.

It is a super-2 number, since 2×165731981² = 54934179052368722, 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 (165731987) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 82865990 + 82865991.

It is an arithmetic number, because the mean of its divisors is an integer number (82865991).

Almost surely, 2^165731981 is an apocalyptic number.

It is an amenable number.

165731981 is a deficient number, since it is larger than the sum of its proper divisors (1).

165731981 is an equidigital number, since it uses as much as digits as its factorization.

165731981 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 45360, while the sum is 41.

The square root of 165731981 is about 12873.6933705911. The cubic root of 165731981 is about 549.2905243197.

The spelling of 165731981 in words is "one hundred sixty-five million, seven hundred thirty-one thousand, nine hundred eighty-one".