81978761 has 2 divisors, whose sum is σ = 81978762. Its totient is φ = 81978760.

The previous prime is 81978751. The next prime is 81978773. The reversal of 81978761 is 16787918.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 55651600 + 26327161 = 7460^2 + 5131^2 .

It is a cyclic number.

It is not a de Polignac number, because 81978761 - 2²² = 77784457 is a prime.

It is not a weakly prime, because it can be changed into another prime (81978751) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40989380 + 40989381.

It is an arithmetic number, because the mean of its divisors is an integer number (40989381).

Almost surely, 2^81978761 is an apocalyptic number.

It is an amenable number.

81978761 is a deficient number, since it is larger than the sum of its proper divisors (1).

81978761 is an equidigital number, since it uses as much as digits as its factorization.

81978761 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 169344, while the sum is 47.

The square root of 81978761 is about 9054.2123345987. The cubic root of 81978761 is about 434.4106362151.

The spelling of 81978761 in words is "eighty-one million, nine hundred seventy-eight thousand, seven hundred sixty-one".