21101100821 has 2 divisors, whose sum is σ = 21101100822. Its totient is φ = 21101100820.

The previous prime is 21101100817. The next prime is 21101100899. The reversal of 21101100821 is 12800110112.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18406348900 + 2694751921 = 135670^2 + 51911^2 .

It is a cyclic number.

It is not a de Polignac number, because 21101100821 - 2² = 21101100817 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21101100821.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21101100421) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10550550410 + 10550550411.

It is an arithmetic number, because the mean of its divisors is an integer number (10550550411).

Almost surely, 2^21101100821 is an apocalyptic number.

It is an amenable number.

21101100821 is a deficient number, since it is larger than the sum of its proper divisors (1).

21101100821 is an equidigital number, since it uses as much as digits as its factorization.

21101100821 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 32, while the sum is 17.

Adding to 21101100821 its reverse (12800110112), we get a palindrome (33901210933).

The spelling of 21101100821 in words is "twenty-one billion, one hundred one million, one hundred thousand, eight hundred twenty-one".