21805101 has 24 divisors (see below), whose sum is σ = 33990840. Its totient is φ = 13418496.

The previous prime is 21805079. The next prime is 21805117. The reversal of 21805101 is 10150812.

It can be written as a sum of positive squares in 4 ways, for example, as 2673225 + 19131876 = 1635^2 + 4374^2 .

It is not a de Polignac number, because 21805101 - 2⁶ = 21805037 is a prime.

It is a super-3 number, since 3×21805101³ (a number of 23 digits) contains 333 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21805181) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 6765 + ... + 9453.

It is an arithmetic number, because the mean of its divisors is an integer number (1416285).

Almost surely, 2^21805101 is an apocalyptic number.

It is an amenable number.

21805101 is a deficient number, since it is larger than the sum of its proper divisors (12185739).

21805101 is a wasteful number, since it uses less digits than its factorization.

21805101 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2765 (or 2762 counting only the distinct ones).

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

The square root of 21805101 is about 4669.5932371032. The cubic root of 21805101 is about 279.3740310463.

Adding to 21805101 its reverse (10150812), we get a palindrome (31955913).

The spelling of 21805101 in words is "twenty-one million, eight hundred five thousand, one hundred one".