19561921 has 8 divisors (see below), whose sum is σ = 20287080. Its totient is φ = 18840192.

The previous prime is 19561909. The next prime is 19561957. The reversal of 19561921 is 12916591.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 5574321 + 13987600 = 2361^2 + 3740^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 19561921 - 2¹⁷ = 19430849 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (19561021) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 18421 + ... + 19453.

It is an arithmetic number, because the mean of its divisors is an integer number (2535885).

Almost surely, 2^19561921 is an apocalyptic number.

It is an amenable number.

19561921 is a deficient number, since it is larger than the sum of its proper divisors (725159).

19561921 is a wasteful number, since it uses less digits than its factorization.

19561921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1715.

The product of its digits is 4860, while the sum is 34.

The square root of 19561921 is about 4422.8860487243. The cubic root of 19561921 is about 269.4452303500.

The spelling of 19561921 in words is "nineteen million, five hundred sixty-one thousand, nine hundred twenty-one".