21100813 has 2 divisors, whose sum is σ = 21100814. Its totient is φ = 21100812.

The previous prime is 21100789. The next prime is 21100823. The reversal of 21100813 is 31800112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19245769 + 1855044 = 4387^2 + 1362^2 .

It is a cyclic number.

It is not a de Polignac number, because 21100813 - 2²¹ = 19003661 is a prime.

21100813 is a modest number, since divided by 813 gives 211 as remainder.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21100823) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10550406 + 10550407.

It is an arithmetic number, because the mean of its divisors is an integer number (10550407).

Almost surely, 2^21100813 is an apocalyptic number.

It is an amenable number.

21100813 is a deficient number, since it is larger than the sum of its proper divisors (1).

21100813 is an equidigital number, since it uses as much as digits as its factorization.

21100813 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 48, while the sum is 16.

The square root of 21100813 is about 4593.5621254099. The cubic root of 21100813 is about 276.3331978479. Note that the first 3 decimals are identical.

Adding to 21100813 its reverse (31800112), we get a palindrome (52900925).

The spelling of 21100813 in words is "twenty-one million, one hundred thousand, eight hundred thirteen".