1561331920 has 80 divisors (see below), whose sum is σ = 3750987600. Its totient is φ = 603942912.

The previous prime is 1561331861. The next prime is 1561331921. The reversal of 1561331920 is 291331651.

It is a happy number.

It can be written as a sum of positive squares in 8 ways, for example, as 45319824 + 1516012096 = 6732^2 + 38936^2 .

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1561331921) 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, 510556 + ... + 513604.

It is an arithmetic number, because the mean of its divisors is an integer number (46887345).

Almost surely, 2^1561331920 is an apocalyptic number.

1561331920 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 1561331920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1875493800).

1561331920 is an abundant number, since it is smaller than the sum of its proper divisors (2189655680).

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

1561331920 is a wasteful number, since it uses less digits than its factorization.

1561331920 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3272 (or 3266 counting only the distinct ones).

The product of its (nonzero) digits is 4860, while the sum is 31.

The square root of 1561331920 is about 39513.6928165415. The cubic root of 1561331920 is about 1160.1079764729.

The spelling of 1561331920 in words is "one billion, five hundred sixty-one million, three hundred thirty-one thousand, nine hundred twenty".