21105801 has 12 divisors (see below), whose sum is σ = 30757428. Its totient is φ = 13945344.

The previous prime is 21105781. The next prime is 21105811. The reversal of 21105801 is 10850112.

It can be written as a sum of positive squares in 2 ways, for example, as 2624400 + 18481401 = 1620^2 + 4299^2 .

It is not a de Polignac number, because 21105801 - 2⁵ = 21105769 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21105811) 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, 9360 + ... + 11393.

It is an arithmetic number, because the mean of its divisors is an integer number (2563119).

Almost surely, 2^21105801 is an apocalyptic number.

It is an amenable number.

21105801 is a deficient number, since it is larger than the sum of its proper divisors (9651627).

21105801 is a wasteful number, since it uses less digits than its factorization.

21105801 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 20872 (or 20869 counting only the distinct ones).

The product of its (nonzero) digits is 80, while the sum is 18.

The square root of 21105801 is about 4594.1050270972. The cubic root of 21105801 is about 276.3549701748.

Adding to 21105801 its reverse (10850112), we get a palindrome (31955913).

The spelling of 21105801 in words is "twenty-one million, one hundred five thousand, eight hundred one".