21720350549 has 4 divisors (see below), whose sum is σ = 21746807340. Its totient is φ = 21693893760.

The previous prime is 21720350521. The next prime is 21720350551. The reversal of 21720350549 is 94505302712.

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 7918330225 + 13802020324 = 88985^2 + 117482^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21720350549 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21720353549) 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, 13227164 + ... + 13228805.

It is an arithmetic number, because the mean of its divisors is an integer number (5436701835).

Almost surely, 2^21720350549 is an apocalyptic number.

It is an amenable number.

21720350549 is a deficient number, since it is larger than the sum of its proper divisors (26456791).

21720350549 is an equidigital number, since it uses as much as digits as its factorization.

21720350549 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 26456790.

The product of its (nonzero) digits is 75600, while the sum is 38.

The spelling of 21720350549 in words is "twenty-one billion, seven hundred twenty million, three hundred fifty thousand, five hundred forty-nine".