81557216789 has 2 divisors, whose sum is σ = 81557216790. Its totient is φ = 81557216788.

The previous prime is 81557216777. The next prime is 81557216801. The reversal of 81557216789 is 98761275518.

It is a balanced prime because it is at equal distance from previous prime (81557216777) and next prime (81557216801).

It can be written as a sum of positive squares in only one way, i.e., 69405902500 + 12151314289 = 263450^2 + 110233^2 .

It is a cyclic number.

It is not a de Polignac number, because 81557216789 - 2⁴ = 81557216773 is a prime.

It is a super-3 number, since 3×81557216789³ (a number of 34 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81557216759) 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, 40778608394 + 40778608395.

It is an arithmetic number, because the mean of its divisors is an integer number (40778608395).

Almost surely, 2^81557216789 is an apocalyptic number.

It is an amenable number.

81557216789 is a deficient number, since it is larger than the sum of its proper divisors (1).

81557216789 is an equidigital number, since it uses as much as digits as its factorization.

81557216789 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 8467200, while the sum is 59.

The spelling of 81557216789 in words is "eighty-one billion, five hundred fifty-seven million, two hundred sixteen thousand, seven hundred eighty-nine".