21724351261 has 4 divisors (see below), whose sum is σ = 21735964224. Its totient is φ = 21712738300.

The previous prime is 21724351217. The next prime is 21724351301. The reversal of 21724351261 is 16215342712.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21724351261 - 2¹⁵ = 21724318493 is a prime.

It is a super-2 number, since 2×21724351261² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21724351661) 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, 5803675 + ... + 5807416.

It is an arithmetic number, because the mean of its divisors is an integer number (5433991056).

Almost surely, 2^21724351261 is an apocalyptic number.

It is an amenable number.

21724351261 is a deficient number, since it is larger than the sum of its proper divisors (11612963).

21724351261 is a wasteful number, since it uses less digits than its factorization.

21724351261 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11612962.

The product of its digits is 20160, while the sum is 34.

Adding to 21724351261 its reverse (16215342712), we get a palindrome (37939693973).

The spelling of 21724351261 in words is "twenty-one billion, seven hundred twenty-four million, three hundred fifty-one thousand, two hundred sixty-one".