21723261 has 16 divisors (see below), whose sum is σ = 33292800. Its totient is φ = 12341808.

The previous prime is 21723257. The next prime is 21723271. The reversal of 21723261 is 16232712.

It is not a de Polignac number, because 21723261 - 2² = 21723257 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21723211) 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, 870 + ... + 6648.

It is an arithmetic number, because the mean of its divisors is an integer number (2080800).

Almost surely, 2^21723261 is an apocalyptic number.

21723261 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21723261 is a deficient number, since it is larger than the sum of its proper divisors (11569539).

21723261 is a wasteful number, since it uses less digits than its factorization.

21723261 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5968.

The product of its digits is 1008, while the sum is 24.

The square root of 21723261 is about 4660.8219232234. The cubic root of 21723261 is about 279.0240726393.

Adding to 21723261 its reverse (16232712), we get a palindrome (37955973).

The spelling of 21723261 in words is "twenty-one million, seven hundred twenty-three thousand, two hundred sixty-one".