21245764561 has 16 divisors (see below), whose sum is σ = 25237586304. Its totient is φ = 17504982144.

The previous prime is 21245764517. The next prime is 21245764619. The reversal of 21245764561 is 16546754212.

It is a cyclic number.

It is not a de Polignac number, because 21245764561 - 2⁹ = 21245764049 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21245764061) 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, 472660 + ... + 515653.

It is an arithmetic number, because the mean of its divisors is an integer number (1577349144).

Almost surely, 2^21245764561 is an apocalyptic number.

It is an amenable number.

21245764561 is a deficient number, since it is larger than the sum of its proper divisors (3991821743).

21245764561 is an equidigital number, since it uses as much as digits as its factorization.

21245764561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 988440.

The product of its digits is 403200, while the sum is 43.

The spelling of 21245764561 in words is "twenty-one billion, two hundred forty-five million, seven hundred sixty-four thousand, five hundred sixty-one".