1561981768 has 8 divisors (see below), whose sum is σ = 2928715830. Its totient is φ = 780990880.

The previous prime is 1561981747. The next prime is 1561981793. The reversal of 1561981768 is 8671891651.

It can be written as a sum of positive squares in only one way, i.e., 1323649924 + 238331844 = 36382^2 + 15438^2 .

It is a tau number, because it is divible by the number of its divisors (8).

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 97623853 + ... + 97623868.

Almost surely, 2^1561981768 is an apocalyptic number.

It is an amenable number.

1561981768 is a deficient number, since it is larger than the sum of its proper divisors (1366734062).

1561981768 is a wasteful number, since it uses less digits than its factorization.

1561981768 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 195247727 (or 195247723 counting only the distinct ones).

The product of its digits is 725760, while the sum is 52.

The square root of 1561981768 is about 39521.9150345729. The cubic root of 1561981768 is about 1160.2689051580.

The spelling of 1561981768 in words is "one billion, five hundred sixty-one million, nine hundred eighty-one thousand, seven hundred sixty-eight".