91781309 has 2 divisors, whose sum is σ = 91781310. Its totient is φ = 91781308.

The previous prime is 91781279. The next prime is 91781311. The reversal of 91781309 is 90318719.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 48511225 + 43270084 = 6965^2 + 6578^2 .

It is an emirp because it is prime and its reverse (90318719) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 91781309 - 2¹⁶ = 91715773 is a prime.

Together with 91781311, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (91781399) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 45890654 + 45890655.

It is an arithmetic number, because the mean of its divisors is an integer number (45890655).

Almost surely, 2^91781309 is an apocalyptic number.

It is an amenable number.

91781309 is a deficient number, since it is larger than the sum of its proper divisors (1).

91781309 is an equidigital number, since it uses as much as digits as its factorization.

91781309 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 13608, while the sum is 38.

The square root of 91781309 is about 9580.2562074299. The cubic root of 91781309 is about 451.0777607096.

The spelling of 91781309 in words is "ninety-one million, seven hundred eighty-one thousand, three hundred nine".