19991920 has 80 divisors (see below), whose sum is σ = 51246720. Its totient is φ = 7206912.

The previous prime is 19991911. The next prime is 19991963. The reversal of 19991920 is 2919991.

It is a tau number, because it is divible by the number of its divisors (80).

It is a Harshad number since it is a multiple of its sum of digits (40).

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, 48676 + ... + 49084.

It is an arithmetic number, because the mean of its divisors is an integer number (640584).

Almost surely, 2^19991920 is an apocalyptic number.

19991920 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 19991920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25623360).

19991920 is an abundant number, since it is smaller than the sum of its proper divisors (31254800).

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

19991920 is a wasteful number, since it uses less digits than its factorization.

19991920 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 482 (or 476 counting only the distinct ones).

The product of its (nonzero) digits is 13122, while the sum is 40.

The square root of 19991920 is about 4471.2324922777. The cubic root of 19991920 is about 271.4052025785.

It can be divided in two parts, 1 and 9991920, that added together give a square (9991921 = 3161²).

The spelling of 19991920 in words is "nineteen million, nine hundred ninety-one thousand, nine hundred twenty".