21680017 has 2 divisors, whose sum is σ = 21680018. Its totient is φ = 21680016.

The previous prime is 21680003. The next prime is 21680027. The reversal of 21680017 is 71008612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21678336 + 1681 = 4656^2 + 41^2 .

It is a cyclic number.

It is not a de Polignac number, because 21680017 - 2¹¹ = 21677969 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21679973 and 21680000.

It is not a weakly prime, because it can be changed into another prime (21680027) 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, 10840008 + 10840009.

It is an arithmetic number, because the mean of its divisors is an integer number (10840009).

Almost surely, 2^21680017 is an apocalyptic number.

It is an amenable number.

21680017 is a deficient number, since it is larger than the sum of its proper divisors (1).

21680017 is an equidigital number, since it uses as much as digits as its factorization.

21680017 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 672, while the sum is 25.

The square root of 21680017 is about 4656.1805162601. The cubic root of 21680017 is about 278.8388006944.

Adding to 21680017 its reverse (71008612), we get a palindrome (92688629).

The spelling of 21680017 in words is "twenty-one million, six hundred eighty thousand, seventeen".