161517821 has 2 divisors, whose sum is σ = 161517822. Its totient is φ = 161517820.

The previous prime is 161517787. The next prime is 161517859. The reversal of 161517821 is 128715161.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 137124100 + 24393721 = 11710^2 + 4939^2 .

It is an emirp because it is prime and its reverse (128715161) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 161517821 - 2²⁶ = 94408957 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (161517121) 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, 80758910 + 80758911.

It is an arithmetic number, because the mean of its divisors is an integer number (80758911).

Almost surely, 2^161517821 is an apocalyptic number.

It is an amenable number.

161517821 is a deficient number, since it is larger than the sum of its proper divisors (1).

161517821 is an equidigital number, since it uses as much as digits as its factorization.

161517821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3360, while the sum is 32.

The square root of 161517821 is about 12708.9661656643. The cubic root of 161517821 is about 544.5947901216.

The spelling of 161517821 in words is "one hundred sixty-one million, five hundred seventeen thousand, eight hundred twenty-one".