391256640 has 168 divisors, whose sum is σ = 1364927928. Its totient is φ = 102850560.

The previous prime is 391256633. The next prime is 391256641. The reversal of 391256640 is 46652193.

It is a happy number.

391256640 is a `hidden beast` number, since 3 + 9 + 1 + 2 + 5 + 6 + 640 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 166464 + 391090176 = 408^2 + 19776^2 .

It is a hoax number, since the sum of its digits (36) coincides with the sum of the digits of its distinct prime factors.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a junction number, because it is equal to n+sod(n) for n = 391256595 and 391256604.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (391256641) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 209310 + ... + 211170.

It is an arithmetic number, because the mean of its divisors is an integer number (8124571).

Almost surely, 2^391256640 is an apocalyptic number.

391256640 is a gapful number since it is divisible by the number (30) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 391256640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (682463964).

391256640 is an abundant number, since it is smaller than the sum of its proper divisors (973671288).

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

391256640 is a wasteful number, since it uses less digits than its factorization.

391256640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1957 (or 1944 counting only the distinct ones).

The product of its (nonzero) digits is 38880, while the sum is 36.

The square root of 391256640 is about 19780.2082901066. The cubic root of 391256640 is about 731.3982333724.

The spelling of 391256640 in words is "three hundred ninety-one million, two hundred fifty-six thousand, six hundred forty".