81720589 has 2 divisors, whose sum is σ = 81720590. Its totient is φ = 81720588.

The previous prime is 81720571. The next prime is 81720599. The reversal of 81720589 is 98502718.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 45118089 + 36602500 = 6717^2 + 6050^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81720589 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81720599) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40860294 + 40860295.

It is an arithmetic number, because the mean of its divisors is an integer number (40860295).

Almost surely, 2^81720589 is an apocalyptic number.

It is an amenable number.

81720589 is a deficient number, since it is larger than the sum of its proper divisors (1).

81720589 is an equidigital number, since it uses as much as digits as its factorization.

81720589 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 40320, while the sum is 40.

The square root of 81720589 is about 9039.9440816855. The cubic root of 81720589 is about 433.9541334158.

The spelling of 81720589 in words is "eighty-one million, seven hundred twenty thousand, five hundred eighty-nine".