161645664681 has 6 divisors (see below), whose sum is σ = 233488182330. Its totient is φ = 107763776448.

The previous prime is 161645664679. The next prime is 161645664683. The reversal of 161645664681 is 186466546161.

161645664681 is a `hidden beast` number, since 1 + 6 + 16 + 4 + 566 + 4 + 68 + 1 = 666.

It is an interprime number because it is at equal distance from previous prime (161645664679) and next prime (161645664683).

It can be written as a sum of positive squares in only one way, i.e., 159920010000 + 1725654681 = 399900^2 + 41541^2 .

It is not a de Polignac number, because 161645664681 - 2¹ = 161645664679 is a prime.

It is a super-4 number, since 4×161645664681⁴ (a number of 46 digits) contains 4444 as substring. Note that it is a super-d number also for d = 2.

It is not an unprimeable number, because it can be changed into a prime (161645664683) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 8980314696 + ... + 8980314713.

It is an arithmetic number, because the mean of its divisors is an integer number (38914697055).

Almost surely, 2^161645664681 is an apocalyptic number.

It is an amenable number.

161645664681 is a deficient number, since it is larger than the sum of its proper divisors (71842517649).

161645664681 is a wasteful number, since it uses less digits than its factorization.

161645664681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 17960629415 (or 17960629412 counting only the distinct ones).

The product of its digits is 4976640, while the sum is 54.

The spelling of 161645664681 in words is "one hundred sixty-one billion, six hundred forty-five million, six hundred sixty-four thousand, six hundred eighty-one".