81239789 has 2 divisors, whose sum is σ = 81239790. Its totient is φ = 81239788.

The previous prime is 81239779. The next prime is 81239797. The reversal of 81239789 is 98793218.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 50879689 + 30360100 = 7133^2 + 5510^2 .

It is a cyclic number.

It is not a de Polignac number, because 81239789 - 2⁸ = 81239533 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81239779) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40619894 + 40619895.

It is an arithmetic number, because the mean of its divisors is an integer number (40619895).

Almost surely, 2^81239789 is an apocalyptic number.

It is an amenable number.

81239789 is a deficient number, since it is larger than the sum of its proper divisors (1).

81239789 is an equidigital number, since it uses as much as digits as its factorization.

81239789 is an evil number, because the sum of its binary digits is even.

The product of its digits is 217728, while the sum is 47.

The square root of 81239789 is about 9013.3117664929. The cubic root of 81239789 is about 433.1014079770.

It can be divided in two parts, 81239 and 789, that added together give a palindrome (82028).

The spelling of 81239789 in words is "eighty-one million, two hundred thirty-nine thousand, seven hundred eighty-nine".