161008721 has 2 divisors, whose sum is σ = 161008722. Its totient is φ = 161008720.

The previous prime is 161008703. The next prime is 161008723. The reversal of 161008721 is 127800161.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 140659600 + 20349121 = 11860^2 + 4511^2 .

It is a cyclic number.

It is not a de Polignac number, because 161008721 - 2²² = 156814417 is a prime.

Together with 161008723, 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 (161008723) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 80504360 + 80504361.

It is an arithmetic number, because the mean of its divisors is an integer number (80504361).

Almost surely, 2^161008721 is an apocalyptic number.

It is an amenable number.

161008721 is a deficient number, since it is larger than the sum of its proper divisors (1).

161008721 is an equidigital number, since it uses as much as digits as its factorization.

161008721 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 672, while the sum is 26.

The square root of 161008721 is about 12688.9211913385. The cubic root of 161008721 is about 544.0220049940.

Adding to 161008721 its reverse (127800161), we get a palindrome (288808882).

The spelling of 161008721 in words is "one hundred sixty-one million, eight thousand, seven hundred twenty-one".