81117249557 has 2 divisors, whose sum is σ = 81117249558. Its totient is φ = 81117249556.

The previous prime is 81117249553. The next prime is 81117249571. The reversal of 81117249557 is 75594271118.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 40678452721 + 40438796836 = 201689^2 + 201094^2 .

It is a cyclic number.

It is not a de Polignac number, because 81117249557 - 2² = 81117249553 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81117249553) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40558624778 + 40558624779.

It is an arithmetic number, because the mean of its divisors is an integer number (40558624779).

Almost surely, 2^81117249557 is an apocalyptic number.

It is an amenable number.

81117249557 is a deficient number, since it is larger than the sum of its proper divisors (1).

81117249557 is an equidigital number, since it uses as much as digits as its factorization.

81117249557 is an evil number, because the sum of its binary digits is even.

The product of its digits is 705600, while the sum is 50.

The spelling of 81117249557 in words is "eighty-one billion, one hundred seventeen million, two hundred forty-nine thousand, five hundred fifty-seven".