81787789 has 2 divisors, whose sum is σ = 81787790. Its totient is φ = 81787788.

The previous prime is 81787777. The next prime is 81787807. The reversal of 81787789 is 98778718.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 76265289 + 5522500 = 8733^2 + 2350^2 .

It is a cyclic number.

It is not a de Polignac number, because 81787789 - 2⁵ = 81787757 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81787759) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40893894 + 40893895.

It is an arithmetic number, because the mean of its divisors is an integer number (40893895).

Almost surely, 2^81787789 is an apocalyptic number.

It is an amenable number.

81787789 is a deficient number, since it is larger than the sum of its proper divisors (1).

81787789 is an equidigital number, since it uses as much as digits as its factorization.

81787789 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1580544, while the sum is 55.

The square root of 81787789 is about 9043.6601550478. The cubic root of 81787789 is about 434.0730497069.

The spelling of 81787789 in words is "eighty-one million, seven hundred eighty-seven thousand, seven hundred eighty-nine".