91728391 has 2 divisors, whose sum is σ = 91728392. Its totient is φ = 91728390.

The previous prime is 91728389. The next prime is 91728407. The reversal of 91728391 is 19382719.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 91728391 - 2¹ = 91728389 is a prime.

Together with 91728389, 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 (91728361) by changing a digit.

It is an upside-down number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 45864195 + 45864196.

It is an arithmetic number, because the mean of its divisors is an integer number (45864196).

Almost surely, 2^91728391 is an apocalyptic number.

91728391 is a deficient number, since it is larger than the sum of its proper divisors (1).

91728391 is an equidigital number, since it uses as much as digits as its factorization.

91728391 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 27216, while the sum is 40.

The square root of 91728391 is about 9577.4939832923. The cubic root of 91728391 is about 450.9910519805.

The spelling of 91728391 in words is "ninety-one million, seven hundred twenty-eight thousand, three hundred ninety-one".