19991000 has 32 divisors (see below), whose sum is σ = 46781280. Its totient is φ = 7996000.

The previous prime is 19990937. The next prime is 19991003. The reversal of 19991000 is 19991.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (19991003) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 8996 + ... + 10995.

It is an arithmetic number, because the mean of its divisors is an integer number (1461915).

Almost surely, 2^19991000 is an apocalyptic number.

19991000 is a gapful number since it is divisible by the number (10) formed by its first and last digit.

It is an amenable number.

19991000 is an abundant number, since it is smaller than the sum of its proper divisors (26790280).

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

19991000 is a wasteful number, since it uses less digits than its factorization.

19991000 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 20012 (or 19998 counting only the distinct ones).

The product of its (nonzero) digits is 729, while the sum is 29.

The square root of 19991000 is about 4471.1296111833. The cubic root of 19991000 is about 271.4010392863.

19991000 divided by its reverse (19991) gives a cube (1000 = 10³).

The spelling of 19991000 in words is "nineteen million, nine hundred ninety-one thousand".