991820712961 has 4 divisors (see below), whose sum is σ = 1068114613972. Its totient is φ = 915526811952.

The previous prime is 991820712937. The next prime is 991820713001. The reversal of 991820712961 is 169217028199.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 169217028199 = 31817 ⋅5318447.

It can be written as a sum of positive squares in 2 ways, for example, as 420351239025 + 571469473936 = 648345^2 + 755956^2 .

It is a cyclic number.

It is not a de Polignac number, because 991820712961 - 2⁵ = 991820712929 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (991820712361) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 38146950486 + ... + 38146950511.

It is an arithmetic number, because the mean of its divisors is an integer number (267028653493).

Almost surely, 2^991820712961 is an apocalyptic number.

It is an amenable number.

991820712961 is a deficient number, since it is larger than the sum of its proper divisors (76293901011).

991820712961 is a wasteful number, since it uses less digits than its factorization.

991820712961 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 76293901010.

The product of its (nonzero) digits is 979776, while the sum is 55.

It can be divided in two parts, 991820 and 712961, that added together give a triangular number (1704781 = T₁₈₄₆).

The spelling of 991820712961 in words is "nine hundred ninety-one billion, eight hundred twenty million, seven hundred twelve thousand, nine hundred sixty-one".