21753261 has 6 divisors (see below), whose sum is σ = 31421390. Its totient is φ = 14502168.

The previous prime is 21753257. The next prime is 21753293. The reversal of 21753261 is 16235712.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 15848361 + 5904900 = 3981^2 + 2430^2 .

It is not a de Polignac number, because 21753261 - 2² = 21753257 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21753961) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1208506 + ... + 1208523.

Almost surely, 2^21753261 is an apocalyptic number.

It is an amenable number.

21753261 is a deficient number, since it is larger than the sum of its proper divisors (9668129).

21753261 is a wasteful number, since it uses less digits than its factorization.

21753261 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2417035 (or 2417032 counting only the distinct ones).

The product of its digits is 2520, while the sum is 27.

The square root of 21753261 is about 4664.0391293384. The cubic root of 21753261 is about 279.1524583942.

Adding to 21753261 its reverse (16235712), we get a palindrome (37988973).

The spelling of 21753261 in words is "twenty-one million, seven hundred fifty-three thousand, two hundred sixty-one".