81771870128449 has 2 divisors, whose sum is σ = 81771870128450. Its totient is φ = 81771870128448.

The previous prime is 81771870128393. The next prime is 81771870128467. The reversal of 81771870128449 is 94482107817718.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 81771870128400 + 49 = 9042780^2 + 7^2 .

It is a cyclic number.

It is not a de Polignac number, because 81771870128449 - 2⁷ = 81771870128321 is a prime.

It is not a weakly prime, because it can be changed into another prime (81771870120449) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40885935064224 + 40885935064225.

It is an arithmetic number, because the mean of its divisors is an integer number (40885935064225).

Almost surely, 2^{81771870128449} is an apocalyptic number.

It is an amenable number.

81771870128449 is a deficient number, since it is larger than the sum of its proper divisors (1).

81771870128449 is an equidigital number, since it uses as much as digits as its factorization.

81771870128449 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 50577408, while the sum is 67.

It can be divided in two parts, 817718701284 and 49, that multiplied together give a square (40068216362916 = 6329946²).

The spelling of 81771870128449 in words is "eighty-one trillion, seven hundred seventy-one billion, eight hundred seventy million, one hundred twenty-eight thousand, four hundred forty-nine".