21319813 has 2 divisors, whose sum is σ = 21319814. Its totient is φ = 21319812.

The previous prime is 21319789. The next prime is 21319817. The reversal of 21319813 is 31891312.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16016004 + 5303809 = 4002^2 + 2303^2 .

It is a cyclic number.

It is not a de Polignac number, because 21319813 - 2⁹ = 21319301 is a prime.

It is equal to p_1348912 and since 21319813 and 1348912 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21319817) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10659906 + 10659907.

It is an arithmetic number, because the mean of its divisors is an integer number (10659907).

Almost surely, 2^21319813 is an apocalyptic number.

It is an amenable number.

21319813 is a deficient number, since it is larger than the sum of its proper divisors (1).

21319813 is an equidigital number, since it uses as much as digits as its factorization.

21319813 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1296, while the sum is 28.

The square root of 21319813 is about 4617.3383025288. The cubic root of 21319813 is about 277.2859068862.

The spelling of 21319813 in words is "twenty-one million, three hundred nineteen thousand, eight hundred thirteen".