19991990 has 32 divisors (see below), whose sum is σ = 38776320. Its totient is φ = 7396704.

The previous prime is 19991989. The next prime is 19992001. The reversal of 19991990 is 9919991.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 6947 + ... + 9393.

It is an arithmetic number, because the mean of its divisors is an integer number (1211760).

Almost surely, 2^19991990 is an apocalyptic number.

19991990 is a gapful number since it is divisible by the number (10) formed by its first and last digit.

19991990 is a deficient number, since it is larger than the sum of its proper divisors (18784330).

19991990 is a wasteful number, since it uses less digits than its factorization.

19991990 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2516.

The product of its (nonzero) digits is 59049, while the sum is 47.

The square root of 19991990 is about 4471.2403200902. The cubic root of 19991990 is about 271.4055193455.

The spelling of 19991990 in words is "nineteen million, nine hundred ninety-one thousand, nine hundred ninety".