172000021 has 2 divisors, whose sum is σ = 172000022. Its totient is φ = 172000020.

The previous prime is 172000019. The next prime is 172000057. The reversal of 172000021 is 120000271.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 90459121 + 81540900 = 9511^2 + 9030^2 .

It is an emirp because it is prime and its reverse (120000271) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 172000021 - 2¹ = 172000019 is a prime.

Together with 172000019, it forms a pair of twin primes.

It is a junction number, because it is equal to n+sod(n) for n = 171999965 and 172000010.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (172000001) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 86000010 + 86000011.

It is an arithmetic number, because the mean of its divisors is an integer number (86000011).

Almost surely, 2^172000021 is an apocalyptic number.

It is an amenable number.

172000021 is a deficient number, since it is larger than the sum of its proper divisors (1).

172000021 is an equidigital number, since it uses as much as digits as its factorization.

172000021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 28, while the sum is 13.

The square root of 172000021 is about 13114.8778492215. The cubic root of 172000021 is about 556.1297992853.

Adding to 172000021 its reverse (120000271), we get a palindrome (292000292).

The spelling of 172000021 in words is "one hundred seventy-two million, twenty-one", and thus it is an aban number.