21653261 has 16 divisors (see below), whose sum is σ = 25374336. Its totient is φ = 18095616.

The previous prime is 21653243. The next prime is 21653267. The reversal of 21653261 is 16235612.

It is not a de Polignac number, because 21653261 - 2⁶ = 21653197 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21653261.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21653267) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 64085 + ... + 64421.

It is an arithmetic number, because the mean of its divisors is an integer number (1585896).

Almost surely, 2^21653261 is an apocalyptic number.

It is an amenable number.

21653261 is a deficient number, since it is larger than the sum of its proper divisors (3721075).

21653261 is a wasteful number, since it uses less digits than its factorization.

21653261 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 548.

The product of its digits is 2160, while the sum is 26.

The square root of 21653261 is about 4653.3064588527. The cubic root of 21653261 is about 278.7240455233.

Adding to 21653261 its reverse (16235612), we get a palindrome (37888873).

The spelling of 21653261 in words is "twenty-one million, six hundred fifty-three thousand, two hundred sixty-one".