81908645513 has 2 divisors, whose sum is σ = 81908645514. Its totient is φ = 81908645512.

The previous prime is 81908645471. The next prime is 81908645527. The reversal of 81908645513 is 31554680918.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 78398320009 + 3510325504 = 279997^2 + 59248^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81908645513 is a prime.

It is not a weakly prime, because it can be changed into another prime (81908645543) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40954322756 + 40954322757.

It is an arithmetic number, because the mean of its divisors is an integer number (40954322757).

Almost surely, 2^81908645513 is an apocalyptic number.

It is an amenable number.

81908645513 is a deficient number, since it is larger than the sum of its proper divisors (1).

81908645513 is an equidigital number, since it uses as much as digits as its factorization.

81908645513 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1036800, while the sum is 50.

The spelling of 81908645513 in words is "eighty-one billion, nine hundred eight million, six hundred forty-five thousand, five hundred thirteen".