21102813 has 12 divisors (see below), whose sum is σ = 30642300. Its totient is φ = 13994496.

The previous prime is 21102761. The next prime is 21102821. The reversal of 21102813 is 31820112.

It can be written as a sum of positive squares in 2 ways, for example, as 14538969 + 6563844 = 3813^2 + 2562^2 .

It is not a de Polignac number, because 21102813 - 2¹⁰ = 21101789 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21102853) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 4338 + ... + 7811.

It is an arithmetic number, because the mean of its divisors is an integer number (2553525).

Almost surely, 2^21102813 is an apocalyptic number.

It is an amenable number.

21102813 is a deficient number, since it is larger than the sum of its proper divisors (9539487).

21102813 is a wasteful number, since it uses less digits than its factorization.

21102813 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12348 (or 12345 counting only the distinct ones).

The product of its (nonzero) digits is 96, while the sum is 18.

The square root of 21102813 is about 4593.7798162298. The cubic root of 21102813 is about 276.3419281424.

Adding to 21102813 its reverse (31820112), we get a palindrome (52922925).

The spelling of 21102813 in words is "twenty-one million, one hundred two thousand, eight hundred thirteen".