21664920749 has 4 divisors (see below), whose sum is σ = 21774895164. Its totient is φ = 21554946336.

The previous prime is 21664920743. The next prime is 21664920793. The reversal of 21664920749 is 94702946612.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 21233735524 + 431185225 = 145718^2 + 20765^2 .

It is a cyclic number.

It is not a de Polignac number, because 21664920749 - 2²⁰ = 21663872173 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21664920697 and 21664920706.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21664920743) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 54986912 + ... + 54987305.

It is an arithmetic number, because the mean of its divisors is an integer number (5443723791).

Almost surely, 2^21664920749 is an apocalyptic number.

It is an amenable number.

21664920749 is a deficient number, since it is larger than the sum of its proper divisors (109974415).

21664920749 is a wasteful number, since it uses less digits than its factorization.

21664920749 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 109974414.

The product of its (nonzero) digits is 1306368, while the sum is 50.

The spelling of 21664920749 in words is "twenty-one billion, six hundred sixty-four million, nine hundred twenty thousand, seven hundred forty-nine".