91720309 has 2 divisors, whose sum is σ = 91720310. Its totient is φ = 91720308.

The previous prime is 91720303. The next prime is 91720361. The reversal of 91720309 is 90302719.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 60606225 + 31114084 = 7785^2 + 5578^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-91720309 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 (91720303) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 45860154 + 45860155.

It is an arithmetic number, because the mean of its divisors is an integer number (45860155).

Almost surely, 2^91720309 is an apocalyptic number.

It is an amenable number.

91720309 is a deficient number, since it is larger than the sum of its proper divisors (1).

91720309 is an equidigital number, since it uses as much as digits as its factorization.

91720309 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3402, while the sum is 31.

The square root of 91720309 is about 9577.0720473431. The cubic root of 91720309 is about 450.9778062933.

It can be divided in two parts, 91720 and 309, that added together give a palindrome (92029).

The spelling of 91720309 in words is "ninety-one million, seven hundred twenty thousand, three hundred nine".