21820171 has 2 divisors, whose sum is σ = 21820172. Its totient is φ = 21820170.

The previous prime is 21820157. The next prime is 21820181. The reversal of 21820171 is 17102812.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21820171 - 2⁹ = 21819659 is a prime.

It is a super-2 number, since 2×21820171² = 952239724938482, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21820111) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10910085 + 10910086.

It is an arithmetic number, because the mean of its divisors is an integer number (10910086).

Almost surely, 2^21820171 is an apocalyptic number.

21820171 is a deficient number, since it is larger than the sum of its proper divisors (1).

21820171 is an equidigital number, since it uses as much as digits as its factorization.

21820171 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 224, while the sum is 22.

The square root of 21820171 is about 4671.2065893086. The cubic root of 21820171 is about 279.4383768020.

Adding to 21820171 its reverse (17102812), we get a palindrome (38922983).

The spelling of 21820171 in words is "twenty-one million, eight hundred twenty thousand, one hundred seventy-one".