20981547557 has 2 divisors, whose sum is σ = 20981547558. Its totient is φ = 20981547556.

The previous prime is 20981547547. The next prime is 20981547569. The reversal of 20981547557 is 75574518902.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 12713464516 + 8268083041 = 112754^2 + 90929^2 .

It is a cyclic number.

It is not a de Polignac number, because 20981547557 - 2⁴ = 20981547541 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 20981547499 and 20981547508.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20981547547) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10490773778 + 10490773779.

It is an arithmetic number, because the mean of its divisors is an integer number (10490773779).

Almost surely, 2^20981547557 is an apocalyptic number.

It is an amenable number.

20981547557 is a deficient number, since it is larger than the sum of its proper divisors (1).

20981547557 is an equidigital number, since it uses as much as digits as its factorization.

20981547557 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 3528000, while the sum is 53.

The spelling of 20981547557 in words is "twenty billion, nine hundred eighty-one million, five hundred forty-seven thousand, five hundred fifty-seven".