991511913681 has 24 divisors (see below), whose sum is σ = 1495416012480. Its totient is φ = 632249925216.

The previous prime is 991511913673. The next prime is 991511913683. The reversal of 991511913681 is 186319115199.

991511913681 is a `hidden beast` number, since 9 + 9 + 1 + 511 + 91 + 36 + 8 + 1 = 666.

It is not a de Polignac number, because 991511913681 - 2³ = 991511913673 is a prime.

It is a super-2 number, since 2×991511913681² (a number of 25 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (991511913683) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 17723925 + ... + 17779778.

It is an arithmetic number, because the mean of its divisors is an integer number (62309000520).

Almost surely, 2^991511913681 is an apocalyptic number.

It is an amenable number.

991511913681 is a deficient number, since it is larger than the sum of its proper divisors (503904098799).

991511913681 is a wasteful number, since it uses less digits than its factorization.

991511913681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 35503845 (or 35503842 counting only the distinct ones).

The product of its digits is 524880, while the sum is 54.

The spelling of 991511913681 in words is "nine hundred ninety-one billion, five hundred eleven million, nine hundred thirteen thousand, six hundred eighty-one".