21084354721 has 16 divisors (see below), whose sum is σ = 21552144208. Its totient is φ = 20621952000.

The previous prime is 21084354713. The next prime is 21084354761. The reversal of 21084354721 is 12745348012.

It is the 59280-th star number.

It can be written as a sum of positive squares in 8 ways, for example, as 3176562321 + 17907792400 = 56361^2 + 133820^2 .

It is a 3-Lehmer number, since φ(21084354721) divides (21084354721-1)³.

It is a cyclic number.

It is not a de Polignac number, because 21084354721 - 2³ = 21084354713 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21084354761) 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 15 ways as a sum of consecutive naturals, for example, 6886531 + ... + 6889591.

It is an arithmetic number, because the mean of its divisors is an integer number (1347009013).

Almost surely, 2^21084354721 is an apocalyptic number.

It is an amenable number.

21084354721 is a deficient number, since it is larger than the sum of its proper divisors (467789487).

21084354721 is a wasteful number, since it uses less digits than its factorization.

21084354721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3892.

The product of its (nonzero) digits is 53760, while the sum is 37.

The spelling of 21084354721 in words is "twenty-one billion, eighty-four million, three hundred fifty-four thousand, seven hundred twenty-one".