172505821 has 2 divisors, whose sum is σ = 172505822. Its totient is φ = 172505820.

The previous prime is 172505779. The next prime is 172505843. The reversal of 172505821 is 128505271.

172505821 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 155900196 + 16605625 = 12486^2 + 4075^2 .

It is a cyclic number.

It is not a de Polignac number, because 172505821 - 2¹⁵ = 172473053 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (172505521) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 86252910 + 86252911.

It is an arithmetic number, because the mean of its divisors is an integer number (86252911).

Almost surely, 2^172505821 is an apocalyptic number.

It is an amenable number.

172505821 is a deficient number, since it is larger than the sum of its proper divisors (1).

172505821 is an equidigital number, since it uses as much as digits as its factorization.

172505821 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 5600, while the sum is 31.

The square root of 172505821 is about 13134.1471363770. The cubic root of 172505821 is about 556.6744022654.

The spelling of 172505821 in words is "one hundred seventy-two million, five hundred five thousand, eight hundred twenty-one".