91815666121 has 3 divisors (see below), whose sum is σ = 91815969133. Its totient is φ = 91815363110.

The previous prime is 91815666097. The next prime is 91815666157. The reversal of 91815666121 is 12166651819.

The square root of 91815666121 is 303011.

It is a perfect power (a square), and thus also a powerful number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 12166651819 = 7 ⋅1738093117.

It is not a de Polignac number, because 91815666121 - 2⁹ = 91815665609 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (91815666161) 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 2 ways as a sum of consecutive naturals, for example, 151506 + ... + 454516.

Almost surely, 2^91815666121 is an apocalyptic number.

91815666121 is the 303011-st square number.

91815666121 is the 151506-th centered octagonal number.

It is an amenable number.

91815666121 is a deficient number, since it is larger than the sum of its proper divisors (303012).

91815666121 is an frugal number, since it uses more digits than its factorization.

91815666121 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 606022 (or 303011 counting only the distinct ones).

The product of its digits is 155520, while the sum is 46.

The spelling of 91815666121 in words is "ninety-one billion, eight hundred fifteen million, six hundred sixty-six thousand, one hundred twenty-one".