19681561 has 4 divisors (see below), whose sum is σ = 19783732. Its totient is φ = 19579392.

The previous prime is 19681553. The next prime is 19681601. The reversal of 19681561 is 16518691.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 3400336 + 16281225 = 1844^2 + 4035^2 .

It is a cyclic number.

It is not a de Polignac number, because 19681561 - 2³ = 19681553 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 19681561.

It is not an unprimeable number, because it can be changed into a prime (19681531) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 50796 + ... + 51181.

It is an arithmetic number, because the mean of its divisors is an integer number (4945933).

Almost surely, 2^19681561 is an apocalyptic number.

It is an amenable number.

19681561 is a deficient number, since it is larger than the sum of its proper divisors (102171).

19681561 is a wasteful number, since it uses less digits than its factorization.

19681561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 102170.

The product of its digits is 12960, while the sum is 37.

The square root of 19681561 is about 4436.3905373626. The cubic root of 19681561 is about 269.9934200500.

The spelling of 19681561 in words is "nineteen million, six hundred eighty-one thousand, five hundred sixty-one".