81421979729 has 2 divisors, whose sum is σ = 81421979730. Its totient is φ = 81421979728.

The previous prime is 81421979719. The next prime is 81421979761. The reversal of 81421979729 is 92797912418.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 78919979329 + 2502000400 = 280927^2 + 50020^2 .

It is a cyclic number.

It is not a de Polignac number, because 81421979729 - 2⁴ = 81421979713 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 (81421979719) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40710989864 + 40710989865.

It is an arithmetic number, because the mean of its divisors is an integer number (40710989865).

Almost surely, 2^81421979729 is an apocalyptic number.

It is an amenable number.

81421979729 is a deficient number, since it is larger than the sum of its proper divisors (1).

81421979729 is an equidigital number, since it uses as much as digits as its factorization.

81421979729 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 4572288, while the sum is 59.

The spelling of 81421979729 in words is "eighty-one billion, four hundred twenty-one million, nine hundred seventy-nine thousand, seven hundred twenty-nine".