20561984 has 28 divisors (see below), whose sum is σ = 41219628. Its totient is φ = 10176000.

The previous prime is 20561927. The next prime is 20561999. The reversal of 20561984 is 48916502.

It can be written as a sum of positive squares in 2 ways, for example, as 11075584 + 9486400 = 3328^2 + 3080^2 .

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4874 + ... + 8054.

Almost surely, 2^20561984 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 20561984, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (20609814).

20561984 is an abundant number, since it is smaller than the sum of its proper divisors (20657644).

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

20561984 is a wasteful number, since it uses less digits than its factorization.

20561984 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3294 (or 3284 counting only the distinct ones).

The product of its (nonzero) digits is 17280, while the sum is 35.

The square root of 20561984 is about 4534.5323904456. The cubic root of 20561984 is about 273.9607452600.

The spelling of 20561984 in words is "twenty million, five hundred sixty-one thousand, nine hundred eighty-four".