21828509561 has 2 divisors, whose sum is σ = 21828509562. Its totient is φ = 21828509560.

The previous prime is 21828509533. The next prime is 21828509579. The reversal of 21828509561 is 16590582812.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16946832400 + 4881677161 = 130180^2 + 69869^2 .

It is a cyclic number.

It is not a de Polignac number, because 21828509561 - 2²⁶ = 21761400697 is a prime.

It is not a weakly prime, because it can be changed into another prime (21828509501) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10914254780 + 10914254781.

It is an arithmetic number, because the mean of its divisors is an integer number (10914254781).

Almost surely, 2^21828509561 is an apocalyptic number.

It is an amenable number.

21828509561 is a deficient number, since it is larger than the sum of its proper divisors (1).

21828509561 is an equidigital number, since it uses as much as digits as its factorization.

21828509561 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 345600, while the sum is 47.

The spelling of 21828509561 in words is "twenty-one billion, eight hundred twenty-eight million, five hundred nine thousand, five hundred sixty-one".