20561717421 has 24 divisors (see below), whose sum is σ = 34159367424. Its totient is φ = 11674709280.

The previous prime is 20561717389. The next prime is 20561717459. The reversal of 20561717421 is 12471716502.

20561717421 is a `hidden beast` number, since 2 + 0 + 5 + 617 + 17 + 4 + 21 = 666.

It is not a de Polignac number, because 20561717421 - 2⁵ = 20561717389 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20561717471) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 1029525 + ... + 1049306.

It is an arithmetic number, because the mean of its divisors is an integer number (1423306976).

Almost surely, 2^20561717421 is an apocalyptic number.

20561717421 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

20561717421 is a deficient number, since it is larger than the sum of its proper divisors (13597650003).

20561717421 is a wasteful number, since it uses less digits than its factorization.

20561717421 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2079001 (or 2078998 counting only the distinct ones).

The product of its (nonzero) digits is 23520, while the sum is 36.

The spelling of 20561717421 in words is "twenty billion, five hundred sixty-one million, seven hundred seventeen thousand, four hundred twenty-one".