81978779 has 2 divisors, whose sum is σ = 81978780. Its totient is φ = 81978778.

The previous prime is 81978773. The next prime is 81978823. The reversal of 81978779 is 97787918.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81978779 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (81978773) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40989389 + 40989390.

It is an arithmetic number, because the mean of its divisors is an integer number (40989390).

Almost surely, 2^81978779 is an apocalyptic number.

81978779 is a deficient number, since it is larger than the sum of its proper divisors (1).

81978779 is an equidigital number, since it uses as much as digits as its factorization.

81978779 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1778112, while the sum is 56.

The square root of 81978779 is about 9054.2133286112. The cubic root of 81978779 is about 434.4106680095.

The spelling of 81978779 in words is "eighty-one million, nine hundred seventy-eight thousand, seven hundred seventy-nine".