172818721 has 2 divisors, whose sum is σ = 172818722. Its totient is φ = 172818720.

The previous prime is 172818713. The next prime is 172818773. The reversal of 172818721 is 127818271.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 153140625 + 19678096 = 12375^2 + 4436^2 .

It is a cyclic number.

It is not a de Polignac number, because 172818721 - 2³ = 172818713 is a prime.

It is not a weakly prime, because it can be changed into another prime (172818791) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 86409360 + 86409361.

It is an arithmetic number, because the mean of its divisors is an integer number (86409361).

Almost surely, 2^172818721 is an apocalyptic number.

It is an amenable number.

172818721 is a deficient number, since it is larger than the sum of its proper divisors (1).

172818721 is an equidigital number, since it uses as much as digits as its factorization.

172818721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 12544, while the sum is 37.

The square root of 172818721 is about 13146.0534381996. The cubic root of 172818721 is about 557.0107739332.

It can be divided in two parts, 1728 and 18721, that added together give a square (20449 = 143²).

The spelling of 172818721 in words is "one hundred seventy-two million, eight hundred eighteen thousand, seven hundred twenty-one".