20561405 has 4 divisors (see below), whose sum is σ = 24673692. Its totient is φ = 16449120.

The previous prime is 20561369. The next prime is 20561407. The reversal of 20561405 is 50416502.

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 6220036 + 14341369 = 2494^2 + 3787^2 .

It is not a de Polignac number, because 20561405 - 2¹⁰ = 20560381 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20561407) 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, 2056136 + ... + 2056145.

It is an arithmetic number, because the mean of its divisors is an integer number (6168423).

Almost surely, 2^20561405 is an apocalyptic number.

It is an amenable number.

20561405 is a deficient number, since it is larger than the sum of its proper divisors (4112287).

20561405 is an equidigital number, since it uses as much as digits as its factorization.

20561405 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4112286.

The product of its (nonzero) digits is 1200, while the sum is 23.

The square root of 20561405 is about 4534.4685465885. The cubic root of 20561405 is about 273.9581737708.

Adding to 20561405 its reverse (50416502), we get a palindrome (70977907).

The spelling of 20561405 in words is "twenty million, five hundred sixty-one thousand, four hundred five".