3991538521971 has 64 divisors (see below), whose sum is σ = 7939657098240. Its totient is φ = 1914024453120.

The previous prime is 3991538521963. The next prime is 3991538522039. The reversal of 3991538521971 is 1791258351993.

3991538521971 is a `hidden beast` number, since 3 + 9 + 9 + 1 + 5 + 38 + 521 + 9 + 71 = 666.

It is not a de Polignac number, because 3991538521971 - 2³ = 3991538521963 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (63).

It is a junction number, because it is equal to n+sod(n) for n = 3991538521899 and 3991538521908.

It is not an unprimeable number, because it can be changed into a prime (3991538521951) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 73816510 + ... + 73870563.

It is an arithmetic number, because the mean of its divisors is an integer number (124057142160).

Almost surely, 2^{3991538521971} is an apocalyptic number.

3991538521971 is a deficient number, since it is larger than the sum of its proper divisors (3948118576269).

3991538521971 is a wasteful number, since it uses less digits than its factorization.

3991538521971 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 147687113 (or 147687107 counting only the distinct ones).

The product of its digits is 18370800, while the sum is 63.

The spelling of 3991538521971 in words is "three trillion, nine hundred ninety-one billion, five hundred thirty-eight million, five hundred twenty-one thousand, nine hundred seventy-one".