1991565408 has 144 divisors (see below), whose sum is σ = 6401747520. Its totient is φ = 539046144.

The previous prime is 1991565397. The next prime is 1991565413. The reversal of 1991565408 is 8045651991.

It is a Harshad number since it is a multiple of its sum of digits (48).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 78235 + ... + 100517.

It is an arithmetic number, because the mean of its divisors is an integer number (44456580).

Almost surely, 2^1991565408 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 1991565408, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (3200873760).

1991565408 is an abundant number, since it is smaller than the sum of its proper divisors (4410182112).

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

1991565408 is a wasteful number, since it uses less digits than its factorization.

1991565408 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 22329 (or 22314 counting only the distinct ones).

The product of its (nonzero) digits is 388800, while the sum is 48.

The square root of 1991565408 is about 44626.9583099722. The cubic root of 1991565408 is about 1258.1474008843.

The spelling of 1991565408 in words is "one billion, nine hundred ninety-one million, five hundred sixty-five thousand, four hundred eight".