21567491749 has 4 divisors (see below), whose sum is σ = 21587046336. Its totient is φ = 21547937164.

The previous prime is 21567491707. The next prime is 21567491761. The reversal of 21567491749 is 94719476512.

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 21567491749 - 2⁹ = 21567491237 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21567491749.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21567491149) 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, 9775639 + ... + 9777844.

It is an arithmetic number, because the mean of its divisors is an integer number (5396761584).

Almost surely, 2^21567491749 is an apocalyptic number.

It is an amenable number.

21567491749 is a deficient number, since it is larger than the sum of its proper divisors (19554587).

21567491749 is a wasteful number, since it uses less digits than its factorization.

21567491749 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 19554586.

The product of its digits is 3810240, while the sum is 55.

The spelling of 21567491749 in words is "twenty-one billion, five hundred sixty-seven million, four hundred ninety-one thousand, seven hundred forty-nine".