161978 has 4 divisors (see below), whose sum is σ = 242970. Its totient is φ = 80988.

The previous prime is 161977. The next prime is 161983. The reversal of 161978 is 879161.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 879161 = 373 ⋅2357.

It can be written as a sum of positive squares in only one way, i.e., 97969 + 64009 = 313^2 + 253^2 .

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (161971) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40493 + ... + 40496.

2¹⁶¹⁹⁷⁸ is an apocalyptic number.

161978 is a deficient number, since it is larger than the sum of its proper divisors (80992).

161978 is an equidigital number, since it uses as much as digits as its factorization.

161978 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 80991.

The product of its digits is 3024, while the sum is 32.

The square root of 161978 is about 402.4649053023. The cubic root of 161978 is about 54.5111499786.

The spelling of 161978 in words is "one hundred sixty-one thousand, nine hundred seventy-eight".