81205977649 has 2 divisors, whose sum is σ = 81205977650. Its totient is φ = 81205977648.

The previous prime is 81205977647. The next prime is 81205977691. The reversal of 81205977649 is 94677950218.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 40750689424 + 40455288225 = 201868^2 + 201135^2 .

It is a cyclic number.

It is not a de Polignac number, because 81205977649 - 2¹ = 81205977647 is a prime.

Together with 81205977647, it forms a pair of twin primes.

It is a junction number, because it is equal to n+sod(n) for n = 81205977593 and 81205977602.

It is not a weakly prime, because it can be changed into another prime (81205977647) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40602988824 + 40602988825.

It is an arithmetic number, because the mean of its divisors is an integer number (40602988825).

Almost surely, 2^81205977649 is an apocalyptic number.

It is an amenable number.

81205977649 is a deficient number, since it is larger than the sum of its proper divisors (1).

81205977649 is an equidigital number, since it uses as much as digits as its factorization.

81205977649 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 7620480, while the sum is 58.

The spelling of 81205977649 in words is "eighty-one billion, two hundred five million, nine hundred seventy-seven thousand, six hundred forty-nine".