21720353549 has 2 divisors, whose sum is σ = 21720353550. Its totient is φ = 21720353548.

The previous prime is 21720353539. The next prime is 21720353609. The reversal of 21720353549 is 94535302712.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17960824324 + 3759529225 = 134018^2 + 61315^2 .

It is a cyclic number.

It is not a de Polignac number, because 21720353549 - 2¹⁶ = 21720288013 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21720353539) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10860176774 + 10860176775.

It is an arithmetic number, because the mean of its divisors is an integer number (10860176775).

Almost surely, 2^21720353549 is an apocalyptic number.

It is an amenable number.

21720353549 is a deficient number, since it is larger than the sum of its proper divisors (1).

21720353549 is an equidigital number, since it uses as much as digits as its factorization.

21720353549 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 226800, while the sum is 41.

The spelling of 21720353549 in words is "twenty-one billion, seven hundred twenty million, three hundred fifty-three thousand, five hundred forty-nine".