20505405621 has 4 divisors (see below), whose sum is σ = 27340540832. Its totient is φ = 13670270412.

The previous prime is 20505405617. The next prime is 20505405623. The reversal of 20505405621 is 12650450502.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 20505405621 - 2² = 20505405617 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 (20505405623) 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, 3417567601 + ... + 3417567606.

It is an arithmetic number, because the mean of its divisors is an integer number (6835135208).

Almost surely, 2^20505405621 is an apocalyptic number.

It is an amenable number.

20505405621 is a deficient number, since it is larger than the sum of its proper divisors (6835135211).

20505405621 is an equidigital number, since it uses as much as digits as its factorization.

20505405621 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6835135210.

The product of its (nonzero) digits is 12000, while the sum is 30.

The spelling of 20505405621 in words is "twenty billion, five hundred five million, four hundred five thousand, six hundred twenty-one".