161661116061581 has 2 divisors, whose sum is σ = 161661116061582. Its totient is φ = 161661116061580.

The previous prime is 161661116061569. The next prime is 161661116061719. The reversal of 161661116061581 is 185160611166161.

161661116061581 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 127141613452681 + 34519502608900 = 11275709^2 + 5875330^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-161661116061581 is a prime.

It is a super-2 number, since 2×161661116061581² (a number of 29 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (161661116361581) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 80830558030790 + 80830558030791.

It is an arithmetic number, because the mean of its divisors is an integer number (80830558030791).

Almost surely, 2^{161661116061581} is an apocalyptic number.

It is an amenable number.

161661116061581 is a deficient number, since it is larger than the sum of its proper divisors (1).

161661116061581 is an equidigital number, since it uses as much as digits as its factorization.

161661116061581 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 311040, while the sum is 50.

The spelling of 161661116061581 in words is "one hundred sixty-one trillion, six hundred sixty-one billion, one hundred sixteen million, sixty-one thousand, five hundred eighty-one".