1991390400 has 336 divisors, whose sum is σ = 7498567680. Its totient is φ = 513561600.

The previous prime is 1991390389. The next prime is 1991390411. The reversal of 1991390400 is 40931991.

It is an interprime number because it is at equal distance from previous prime (1991390389) and next prime (1991390411).

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

It is an unprimeable number.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 1338457 + ... + 1339943.

Almost surely, 2^1991390400 is an apocalyptic number.

1991390400 is a gapful number since it is divisible by the number (10) 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 1991390400, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (3749283840).

1991390400 is an abundant number, since it is smaller than the sum of its proper divisors (5507177280).

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

1991390400 is a wasteful number, since it uses less digits than its factorization.

1991390400 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1549 (or 1528 counting only the distinct ones).

The product of its (nonzero) digits is 8748, while the sum is 36.

The square root of 1991390400 is about 44624.9974789915. The cubic root of 1991390400 is about 1258.1105467411.

The spelling of 1991390400 in words is "one billion, nine hundred ninety-one million, three hundred ninety thousand, four hundred".