19991640 has 32 divisors (see below), whose sum is σ = 59975280. Its totient is φ = 5331072.

The previous prime is 19991639. The next prime is 19991651. The reversal of 19991640 is 4619991.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 83179 + ... + 83418.

Almost surely, 2^19991640 is an apocalyptic number.

19991640 is a gapful number since it is divisible by the number (10) formed by its first and last digit.

It is an amenable number.

19991640 is an abundant number, since it is smaller than the sum of its proper divisors (39983640).

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

19991640 is a wasteful number, since it uses less digits than its factorization.

19991640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 166611 (or 166607 counting only the distinct ones).

The product of its (nonzero) digits is 17496, while the sum is 39.

The square root of 19991640 is about 4471.2011808909. The cubic root of 19991640 is about 271.4039355031.

The spelling of 19991640 in words is "nineteen million, nine hundred ninety-one thousand, six hundred forty".