161668721 has 2 divisors, whose sum is σ = 161668722. Its totient is φ = 161668720.

The previous prime is 161668667. The next prime is 161668723. The reversal of 161668721 is 127866161.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 147501025 + 14167696 = 12145^2 + 3764^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-161668721 is a prime.

It is a super-2 number, since 2×161668721² = 52273550699551682, which contains 22 as substring.

Together with 161668723, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (161668723) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 80834360 + 80834361.

It is an arithmetic number, because the mean of its divisors is an integer number (80834361).

Almost surely, 2^161668721 is an apocalyptic number.

It is an amenable number.

161668721 is a deficient number, since it is larger than the sum of its proper divisors (1).

161668721 is an equidigital number, since it uses as much as digits as its factorization.

161668721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 24192, while the sum is 38.

The square root of 161668721 is about 12714.9015332404. The cubic root of 161668721 is about 544.7643354474.

The spelling of 161668721 in words is "one hundred sixty-one million, six hundred sixty-eight thousand, seven hundred twenty-one".