161031781 has 2 divisors, whose sum is σ = 161031782. Its totient is φ = 161031780.

The previous prime is 161031779. The next prime is 161031817. The reversal of 161031781 is 187130161.

Together with next prime (161031817) it forms an Ormiston pair, because they use the same digits, order apart.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 158986881 + 2044900 = 12609^2 + 1430^2 .

It is an emirp because it is prime and its reverse (187130161) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 161031781 - 2¹ = 161031779 is a prime.

It is a super-2 number, since 2×161031781² = 51862468984063922, which contains 22 as substring.

Together with 161031779, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (161031721) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 80515890 + 80515891.

It is an arithmetic number, because the mean of its divisors is an integer number (80515891).

Almost surely, 2^161031781 is an apocalyptic number.

It is an amenable number.

161031781 is a deficient number, since it is larger than the sum of its proper divisors (1).

161031781 is an equidigital number, since it uses as much as digits as its factorization.

161031781 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1008, while the sum is 28.

The square root of 161031781 is about 12689.8298254941. The cubic root of 161031781 is about 544.0479757375.

The spelling of 161031781 in words is "one hundred sixty-one million, thirty-one thousand, seven hundred eighty-one".