168991981 has 8 divisors (see below), whose sum is σ = 171457920. Its totient is φ = 166534368.

The previous prime is 168991973. The next prime is 168992027. The reversal of 168991981 is 189199861.

168991981 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 168991981 - 2³ = 168991973 is a prime.

It is a super-2 number, since 2×168991981² = 57116579284608722, 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 (168991481) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 47010 + ... + 50476.

It is an arithmetic number, because the mean of its divisors is an integer number (21432240).

Almost surely, 2^168991981 is an apocalyptic number.

It is an amenable number.

168991981 is a deficient number, since it is larger than the sum of its proper divisors (2465939).

168991981 is an equidigital number, since it uses as much as digits as its factorization.

168991981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4163.

The product of its digits is 279936, while the sum is 52.

The square root of 168991981 is about 12999.6915732643. The cubic root of 168991981 is about 552.8687366053.

It can be divided in two parts, 1689919 and 81, that added together give a square (1690000 = 1300²).

The spelling of 168991981 in words is "one hundred sixty-eight million, nine hundred ninety-one thousand, nine hundred eighty-one".