165517981 has 2 divisors, whose sum is σ = 165517982. Its totient is φ = 165517980.

The previous prime is 165517907. The next prime is 165518029. The reversal of 165517981 is 189715561.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 158004900 + 7513081 = 12570^2 + 2741^2 .

It is a cyclic number.

It is not a de Polignac number, because 165517981 - 2¹³ = 165509789 is a prime.

It is a super-2 number, since 2×165517981² = 54792404068632722, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (165511981) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 82758990 + 82758991.

It is an arithmetic number, because the mean of its divisors is an integer number (82758991).

Almost surely, 2^165517981 is an apocalyptic number.

It is an amenable number.

165517981 is a deficient number, since it is larger than the sum of its proper divisors (1).

165517981 is an equidigital number, since it uses as much as digits as its factorization.

165517981 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 75600, while the sum is 43.

The square root of 165517981 is about 12865.3791626986. The cubic root of 165517981 is about 549.0540002601.

The spelling of 165517981 in words is "one hundred sixty-five million, five hundred seventeen thousand, nine hundred eighty-one".