81978773 has 2 divisors, whose sum is σ = 81978774. Its totient is φ = 81978772.

The previous prime is 81978761. The next prime is 81978779. The reversal of 81978773 is 37787918.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 76702564 + 5276209 = 8758^2 + 2297^2 .

It is a cyclic number.

It is not a de Polignac number, because 81978773 - 2¹⁸ = 81716629 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81978779) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40989386 + 40989387.

It is an arithmetic number, because the mean of its divisors is an integer number (40989387).

Almost surely, 2^81978773 is an apocalyptic number.

It is an amenable number.

81978773 is a deficient number, since it is larger than the sum of its proper divisors (1).

81978773 is an equidigital number, since it uses as much as digits as its factorization.

81978773 is an evil number, because the sum of its binary digits is even.

The product of its digits is 592704, while the sum is 50.

The square root of 81978773 is about 9054.2129972737. The cubic root of 81978773 is about 434.4106574113.

The spelling of 81978773 in words is "eighty-one million, nine hundred seventy-eight thousand, seven hundred seventy-three".