21105261 has 12 divisors (see below), whose sum is σ = 30709692. Its totient is φ = 13966656.

The previous prime is 21105239. The next prime is 21105307. The reversal of 21105261 is 16250112.

It can be written as a sum of positive squares in 2 ways, for example, as 4040100 + 17065161 = 2010^2 + 4131^2 .

It is not a de Polignac number, because 21105261 - 2⁵ = 21105229 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 (21105221) 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, 7326 + ... + 9791.

It is an arithmetic number, because the mean of its divisors is an integer number (2559141).

Almost surely, 2^21105261 is an apocalyptic number.

It is an amenable number.

21105261 is a deficient number, since it is larger than the sum of its proper divisors (9604431).

21105261 is a wasteful number, since it uses less digits than its factorization.

21105261 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 17260 (or 17257 counting only the distinct ones).

The product of its (nonzero) digits is 120, while the sum is 18.

The square root of 21105261 is about 4594.0462557532. The cubic root of 21105261 is about 276.3526132721.

Adding to 21105261 its reverse (16250112), we get a palindrome (37355373).

The spelling of 21105261 in words is "twenty-one million, one hundred five thousand, two hundred sixty-one".