21381317 has 2 divisors, whose sum is σ = 21381318. Its totient is φ = 21381316.

The previous prime is 21381307. The next prime is 21381361. The reversal of 21381317 is 71318312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16924996 + 4456321 = 4114^2 + 2111^2 .

It is a cyclic number.

It is not a de Polignac number, because 21381317 - 2¹⁸ = 21119173 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21381307) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10690658 + 10690659.

It is an arithmetic number, because the mean of its divisors is an integer number (10690659).

Almost surely, 2^21381317 is an apocalyptic number.

It is an amenable number.

21381317 is a deficient number, since it is larger than the sum of its proper divisors (1).

21381317 is an equidigital number, since it uses as much as digits as its factorization.

21381317 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1008, while the sum is 26.

The square root of 21381317 is about 4623.9936202378. The cubic root of 21381317 is about 277.5522916363.

Adding to 21381317 its reverse (71318312), we get a palindrome (92699629).

The spelling of 21381317 in words is "twenty-one million, three hundred eighty-one thousand, three hundred seventeen".