165917981 has 4 divisors (see below), whose sum is σ = 165967872. Its totient is φ = 165868092.

The previous prime is 165917957. The next prime is 165918031. The reversal of 165917981 is 189719561.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-165917981 is a prime.

It is a super-2 number, since 2×165917981² = 55057552838232722, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (165917881) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 19571 + ... + 26736.

It is an arithmetic number, because the mean of its divisors is an integer number (41491968).

Almost surely, 2^165917981 is an apocalyptic number.

It is an amenable number.

165917981 is a deficient number, since it is larger than the sum of its proper divisors (49891).

165917981 is an equidigital number, since it uses as much as digits as its factorization.

165917981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 49890.

The product of its digits is 136080, while the sum is 47.

The square root of 165917981 is about 12880.9153789628. The cubic root of 165917981 is about 549.4959359726.

The spelling of 165917981 in words is "one hundred sixty-five million, nine hundred seventeen thousand, nine hundred eighty-one".