21261 has 8 divisors (see below), whose sum is σ = 29920. Its totient is φ = 13392.

The previous prime is 21247. The next prime is 21269. The reversal of 21261 is 16212.

21261 = 24² + 25² + ... + 42².

21261 is nontrivially palindromic in base 8.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21261 - 2⁹ = 20749 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 (21269) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 130 + ... + 243.

It is an arithmetic number, because the mean of its divisors is an integer number (3740).

2²¹²⁶¹ is an apocalyptic number.

It is an amenable number.

21261 is a deficient number, since it is larger than the sum of its proper divisors (8659).

21261 is a wasteful number, since it uses less digits than its factorization.

21261 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 395.

The product of its digits is 24, while the sum is 12.

The square root of 21261 is about 145.8115221785. The cubic root of 21261 is about 27.7030697723.

Adding to 21261 its reverse (16212), we get a palindrome (37473).

It can be divided in two parts, 21 and 261, that added together give a palindrome (282).

The spelling of 21261 in words is "twenty-one thousand, two hundred sixty-one".