20505709751 has 4 divisors (see below), whose sum is σ = 20523873600. Its totient is φ = 20487545904.

The previous prime is 20505709747. The next prime is 20505709771. The reversal of 20505709751 is 15790750502.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 20505709751 - 2² = 20505709747 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 20505709699 and 20505709708.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20505709711) 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, 9080231 + ... + 9082488.

It is an arithmetic number, because the mean of its divisors is an integer number (5130968400).

Almost surely, 2^20505709751 is an apocalyptic number.

20505709751 is a deficient number, since it is larger than the sum of its proper divisors (18163849).

20505709751 is a wasteful number, since it uses less digits than its factorization.

20505709751 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18163848.

The product of its (nonzero) digits is 110250, while the sum is 41.

The spelling of 20505709751 in words is "twenty billion, five hundred five million, seven hundred nine thousand, seven hundred fifty-one".