81644525881 has 2 divisors, whose sum is σ = 81644525882. Its totient is φ = 81644525880.

The previous prime is 81644525861. The next prime is 81644525917. The reversal of 81644525881 is 18852544618.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 74588525881 + 7056000000 = 273109^2 + 84000^2 .

It is a cyclic number.

It is not a de Polignac number, because 81644525881 - 2⁵ = 81644525849 is a prime.

It is a super-2 number, since 2×81644525881² (a number of 23 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (81644525821) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40822262940 + 40822262941.

It is an arithmetic number, because the mean of its divisors is an integer number (40822262941).

Almost surely, 2^81644525881 is an apocalyptic number.

It is an amenable number.

81644525881 is a deficient number, since it is larger than the sum of its proper divisors (1).

81644525881 is an equidigital number, since it uses as much as digits as its factorization.

81644525881 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2457600, while the sum is 52.

The spelling of 81644525881 in words is "eighty-one billion, six hundred forty-four million, five hundred twenty-five thousand, eight hundred eighty-one".