81685289591 has 2 divisors, whose sum is σ = 81685289592. Its totient is φ = 81685289590.

The previous prime is 81685289563. The next prime is 81685289603. The reversal of 81685289591 is 19598258618.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 81685289591 - 2¹⁸ = 81685027447 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81685289891) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40842644795 + 40842644796.

It is an arithmetic number, because the mean of its divisors is an integer number (40842644796).

Almost surely, 2^81685289591 is an apocalyptic number.

81685289591 is a deficient number, since it is larger than the sum of its proper divisors (1).

81685289591 is an equidigital number, since it uses as much as digits as its factorization.

81685289591 is an evil number, because the sum of its binary digits is even.

The product of its digits is 12441600, while the sum is 62.

The spelling of 81685289591 in words is "eighty-one billion, six hundred eighty-five million, two hundred eighty-nine thousand, five hundred ninety-one".