21218317 has 2 divisors, whose sum is σ = 21218318. Its totient is φ = 21218316.

The previous prime is 21218311. The next prime is 21218321. The reversal of 21218317 is 71381212.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12152196 + 9066121 = 3486^2 + 3011^2 .

It is a cyclic number.

It is not a de Polignac number, because 21218317 - 2⁷ = 21218189 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21218291 and 21218300.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21218311) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10609158 + 10609159.

It is an arithmetic number, because the mean of its divisors is an integer number (10609159).

Almost surely, 2^21218317 is an apocalyptic number.

It is an amenable number.

21218317 is a deficient number, since it is larger than the sum of its proper divisors (1).

21218317 is an equidigital number, since it uses as much as digits as its factorization.

21218317 is an evil number, because the sum of its binary digits is even.

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

The square root of 21218317 is about 4606.3344429166. The cubic root of 21218317 is about 276.8451871179.

Adding to 21218317 its reverse (71381212), we get a palindrome (92599529).

The spelling of 21218317 in words is "twenty-one million, two hundred eighteen thousand, three hundred seventeen".