1991761920 has 224 divisors, whose sum is σ = 7085319840. Its totient is φ = 530841600.

The previous prime is 1991761913. The next prime is 1991761927. The reversal of 1991761920 is 291671991.

1991761920 is a `hidden beast` number, since 1 + 9 + 9 + 1 + 7 + 619 + 20 = 666.

It is an interprime number because it is at equal distance from previous prime (1991761913) and next prime (1991761927).

It is a Harshad number since it is a multiple of its sum of digits (45).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1991761927) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1105020 + ... + 1106820.

Almost surely, 2^1991761920 is an apocalyptic number.

1991761920 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 1991761920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (3542659920).

1991761920 is an abundant number, since it is smaller than the sum of its proper divisors (5093557920).

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

1991761920 is an equidigital number, since it uses as much as digits as its factorization.

1991761920 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1841 (or 1811 counting only the distinct ones).

The product of its (nonzero) digits is 61236, while the sum is 45.

The square root of 1991761920 is about 44629.1599741694. The cubic root of 1991761920 is about 1258.1887808844.

The spelling of 1991761920 in words is "one billion, nine hundred ninety-one million, seven hundred sixty-one thousand, nine hundred twenty".