81374776781 has 2 divisors, whose sum is σ = 81374776782. Its totient is φ = 81374776780.

The previous prime is 81374776771. The next prime is 81374776787. The reversal of 81374776781 is 18767747318.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 73747549225 + 7627227556 = 271565^2 + 87334^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81374776781 is a prime.

It is a super-2 number, since 2×81374776781² (a number of 23 digits) contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 81374776781.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81374776787) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40687388390 + 40687388391.

It is an arithmetic number, because the mean of its divisors is an integer number (40687388391).

Almost surely, 2^81374776781 is an apocalyptic number.

It is an amenable number.

81374776781 is a deficient number, since it is larger than the sum of its proper divisors (1).

81374776781 is an equidigital number, since it uses as much as digits as its factorization.

81374776781 is an evil number, because the sum of its binary digits is even.

The product of its digits is 11063808, while the sum is 59.

The spelling of 81374776781 in words is "eighty-one billion, three hundred seventy-four million, seven hundred seventy-six thousand, seven hundred eighty-one".