27781538021 has 2 divisors, whose sum is σ = 27781538022. Its totient is φ = 27781538020.

The previous prime is 27781538003. The next prime is 27781538051. The reversal of 27781538021 is 12083518772.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 24261489121 + 3520048900 = 155761^2 + 59330^2 .

It is a cyclic number.

It is not a de Polignac number, because 27781538021 - 2¹⁸ = 27781275877 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (27781538051) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 13890769010 + 13890769011.

It is an arithmetic number, because the mean of its divisors is an integer number (13890769011).

Almost surely, 2^27781538021 is an apocalyptic number.

It is an amenable number.

27781538021 is a deficient number, since it is larger than the sum of its proper divisors (1).

27781538021 is an equidigital number, since it uses as much as digits as its factorization.

27781538021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 188160, while the sum is 44.

The spelling of 27781538021 in words is "twenty-seven billion, seven hundred eighty-one million, five hundred thirty-eight thousand, twenty-one".