21821261 has 12 divisors (see below), whose sum is σ = 27412896. Its totient is φ = 17002920.

The previous prime is 21821257. The next prime is 21821263. The reversal of 21821261 is 16212812.

It is not a de Polignac number, because 21821261 - 2² = 21821257 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21821263) 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, 12035 + ... + 13728.

It is an arithmetic number, because the mean of its divisors is an integer number (2284408).

Almost surely, 2^21821261 is an apocalyptic number.

It is an amenable number.

21821261 is a deficient number, since it is larger than the sum of its proper divisors (5591635).

21821261 is a wasteful number, since it uses less digits than its factorization.

21821261 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 25792 (or 25781 counting only the distinct ones).

The product of its digits is 384, while the sum is 23.

The square root of 21821261 is about 4671.3232600624. The cubic root of 21821261 is about 279.4430297255.

It can be divided in two parts, 2182 and 1261, that added together give a palindrome (3443).

The spelling of 21821261 in words is "twenty-one million, eight hundred twenty-one thousand, two hundred sixty-one".