161778681 has 16 divisors (see below), whose sum is σ = 253771200. Its totient is φ = 101507904.

The previous prime is 161778671. The next prime is 161778713. The reversal of 161778681 is 186877161.

It is a happy number.

It is not a de Polignac number, because 161778681 - 2¹⁰ = 161777657 is a prime.

It is a super-2 number, since 2×161778681² = 52344683252199522, which contains 22 as substring.

It is a Smith number, since the sum of its digits (45) coincides with the sum of the digits of its prime factors.

It is not an unprimeable number, because it can be changed into a prime (161778611) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 175771 + ... + 176688.

It is an arithmetic number, because the mean of its divisors is an integer number (15860700).

Almost surely, 2^161778681 is an apocalyptic number.

It is an amenable number.

161778681 is a deficient number, since it is larger than the sum of its proper divisors (91992519).

161778681 is a wasteful number, since it uses less digits than its factorization.

161778681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 352485 (or 352479 counting only the distinct ones).

The product of its digits is 112896, while the sum is 45.

The square root of 161778681 is about 12719.2248584574. The cubic root of 161778681 is about 544.8878157556.

The spelling of 161778681 in words is "one hundred sixty-one million, seven hundred seventy-eight thousand, six hundred eighty-one".