21013261 has 4 divisors (see below), whose sum is σ = 21122332. Its totient is φ = 20904192.

The previous prime is 21013249. The next prime is 21013271. The reversal of 21013261 is 16231012.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 12638025 + 8375236 = 3555^2 + 2894^2 .

It is a cyclic number.

It is not a de Polignac number, because 21013261 - 2⁹ = 21012749 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 (21013271) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 54246 + ... + 54631.

It is an arithmetic number, because the mean of its divisors is an integer number (5280583).

Almost surely, 2^21013261 is an apocalyptic number.

It is an amenable number.

21013261 is a deficient number, since it is larger than the sum of its proper divisors (109071).

21013261 is a wasteful number, since it uses less digits than its factorization.

21013261 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 109070.

The product of its (nonzero) digits is 72, while the sum is 16.

The square root of 21013261 is about 4584.0223603294. The cubic root of 21013261 is about 275.9504785827.

Adding to 21013261 its reverse (16231012), we get a palindrome (37244273).

The spelling of 21013261 in words is "twenty-one million, thirteen thousand, two hundred sixty-one".