81779989 has 2 divisors, whose sum is σ = 81779990. Its totient is φ = 81779988.

The previous prime is 81779987. The next prime is 81780011. The reversal of 81779989 is 98997718.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 81595089 + 184900 = 9033^2 + 430^2 .

It is a cyclic number.

It is not a de Polignac number, because 81779989 - 2¹ = 81779987 is a prime.

Together with 81779987, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81779987) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40889994 + 40889995.

It is an arithmetic number, because the mean of its divisors is an integer number (40889995).

Almost surely, 2^81779989 is an apocalyptic number.

It is an amenable number.

81779989 is a deficient number, since it is larger than the sum of its proper divisors (1).

81779989 is an equidigital number, since it uses as much as digits as its factorization.

81779989 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2286144, while the sum is 58.

The square root of 81779989 is about 9043.2289034393. The cubic root of 81779989 is about 434.0592502655.

The spelling of 81779989 in words is "eighty-one million, seven hundred seventy-nine thousand, nine hundred eighty-nine".