21531317 has 2 divisors, whose sum is σ = 21531318. Its totient is φ = 21531316.

The previous prime is 21531269. The next prime is 21531337. The reversal of 21531317 is 71313512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12716356 + 8814961 = 3566^2 + 2969^2 .

It is a cyclic number.

It is not a de Polignac number, because 21531317 - 2¹⁰ = 21530293 is a prime.

It is a super-2 number, since 2×21531317² = 927195223508978, which contains 22 as substring.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 21531292 and 21531301.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21531337) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10765658 + 10765659.

It is an arithmetic number, because the mean of its divisors is an integer number (10765659).

Almost surely, 2^21531317 is an apocalyptic number.

It is an amenable number.

21531317 is a deficient number, since it is larger than the sum of its proper divisors (1).

21531317 is an equidigital number, since it uses as much as digits as its factorization.

21531317 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 630, while the sum is 23.

The square root of 21531317 is about 4640.1850178630. The cubic root of 21531317 is about 278.1998330301.

Adding to 21531317 its reverse (71313512), we get a palindrome (92844829).

The spelling of 21531317 in words is "twenty-one million, five hundred thirty-one thousand, three hundred seventeen".