161288721 has 24 divisors (see below), whose sum is σ = 255307104. Its totient is φ = 97306560.

The previous prime is 161288683. The next prime is 161288747. The reversal of 161288721 is 127882161.

It is not a de Polignac number, because 161288721 - 2¹⁰ = 161287697 is a prime.

It is not an unprimeable number, because it can be changed into a prime (161288761) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 18885 + ... + 26061.

It is an arithmetic number, because the mean of its divisors is an integer number (10637796).

Almost surely, 2^161288721 is an apocalyptic number.

161288721 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

161288721 is a deficient number, since it is larger than the sum of its proper divisors (94018383).

161288721 is a wasteful number, since it uses less digits than its factorization.

161288721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7421 (or 7418 counting only the distinct ones).

The product of its digits is 10752, while the sum is 36.

The square root of 161288721 is about 12699.9496455695. The cubic root of 161288721 is about 544.3371803573.

It can be divided in two parts, 161 and 288721, that added together give a palindrome (288882).

The spelling of 161288721 in words is "one hundred sixty-one million, two hundred eighty-eight thousand, seven hundred twenty-one".