31891987 has 4 divisors (see below), whose sum is σ = 31910760. Its totient is φ = 31873216.

The previous prime is 31891943. The next prime is 31891997. The reversal of 31891987 is 78919813.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 78919813 = 7 ⋅11274259.

It is a cyclic number.

It is not a de Polignac number, because 31891987 - 2¹¹ = 31889939 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (31891927) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 6553 + ... + 10330.

It is an arithmetic number, because the mean of its divisors is an integer number (7977690).

Almost surely, 2^31891987 is an apocalyptic number.

31891987 is a deficient number, since it is larger than the sum of its proper divisors (18773).

31891987 is a wasteful number, since it uses less digits than its factorization.

31891987 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18772.

The product of its digits is 108864, while the sum is 46.

The square root of 31891987 is about 5647.2990889451. The cubic root of 31891987 is about 317.1225995018.

The spelling of 31891987 in words is "thirty-one million, eight hundred ninety-one thousand, nine hundred eighty-seven".