91781821 has 8 divisors (see below), whose sum is σ = 94147704. Its totient is φ = 89422080.

The previous prime is 91781819. The next prime is 91781857. The reversal of 91781821 is 12818719.

It can be written as a sum of positive squares in 4 ways, for example, as 1265625 + 90516196 = 1125^2 + 9514^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 91781821 - 2¹ = 91781819 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (91781801) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 51481 + ... + 53233.

It is an arithmetic number, because the mean of its divisors is an integer number (11768463).

Almost surely, 2^91781821 is an apocalyptic number.

It is an amenable number.

91781821 is a deficient number, since it is larger than the sum of its proper divisors (2365883).

91781821 is a wasteful number, since it uses less digits than its factorization.

91781821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3071.

The product of its digits is 8064, while the sum is 37.

The square root of 91781821 is about 9580.2829290162. The cubic root of 91781821 is about 451.0785994839.

The spelling of 91781821 in words is "ninety-one million, seven hundred eighty-one thousand, eight hundred twenty-one".