3991518 has 48 divisors (see below), whose sum is σ = 9225216. Its totient is φ = 1292760.

The previous prime is 3991517. The next prime is 3991543. The reversal of 3991518 is 8151993.

It is a happy number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (3991511) 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, 20803 + ... + 20993.

It is an arithmetic number, because the mean of its divisors is an integer number (192192).

Almost surely, 2^3991518 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 3991518, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (4612608).

3991518 is an abundant number, since it is smaller than the sum of its proper divisors (5233698).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

3991518 is a wasteful number, since it uses less digits than its factorization.

3991518 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 251 (or 239 counting only the distinct ones).

The product of its digits is 9720, while the sum is 36.

The square root of 3991518 is about 1997.8783746765. The cubic root of 3991518 is about 158.6278229969.

The spelling of 3991518 in words is "three million, nine hundred ninety-one thousand, five hundred eighteen".