81974683649 has 2 divisors, whose sum is σ = 81974683650. Its totient is φ = 81974683648.

The previous prime is 81974683643. The next prime is 81974683657. The reversal of 81974683649 is 94638647918.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 80528250625 + 1446433024 = 283775^2 + 38032^2 .

It is a cyclic number.

It is not a de Polignac number, because 81974683649 - 2⁴ = 81974683633 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (81974683643) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40987341824 + 40987341825.

It is an arithmetic number, because the mean of its divisors is an integer number (40987341825).

Almost surely, 2^81974683649 is an apocalyptic number.

It is an amenable number.

81974683649 is a deficient number, since it is larger than the sum of its proper divisors (1).

81974683649 is an equidigital number, since it uses as much as digits as its factorization.

81974683649 is an evil number, because the sum of its binary digits is even.

The product of its digits is 62705664, while the sum is 65.

The spelling of 81974683649 in words is "eighty-one billion, nine hundred seventy-four million, six hundred eighty-three thousand, six hundred forty-nine".