20720839661 has 4 divisors (see below), whose sum is σ = 20723348352. Its totient is φ = 20718330972.

The previous prime is 20720839651. The next prime is 20720839739. The reversal of 20720839661 is 16693802702.

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 a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20720839661 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20720839631) 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, 1241915 + ... + 1258488.

It is an arithmetic number, because the mean of its divisors is an integer number (5180837088).

Almost surely, 2^20720839661 is an apocalyptic number.

It is an amenable number.

20720839661 is a deficient number, since it is larger than the sum of its proper divisors (2508691).

20720839661 is an equidigital number, since it uses as much as digits as its factorization.

20720839661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2508690.

The product of its (nonzero) digits is 217728, while the sum is 44.

The spelling of 20720839661 in words is "twenty billion, seven hundred twenty million, eight hundred thirty-nine thousand, six hundred sixty-one".