20784989921 has 2 divisors, whose sum is σ = 20784989922. Its totient is φ = 20784989920.

The previous prime is 20784989917. The next prime is 20784989933. The reversal of 20784989921 is 12998948702.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19499050321 + 1285939600 = 139639^2 + 35860^2 .

It is a cyclic number.

It is not a de Polignac number, because 20784989921 - 2² = 20784989917 is a prime.

It is not a weakly prime, because it can be changed into another prime (20784989521) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10392494960 + 10392494961.

It is an arithmetic number, because the mean of its divisors is an integer number (10392494961).

Almost surely, 2^20784989921 is an apocalyptic number.

It is an amenable number.

20784989921 is a deficient number, since it is larger than the sum of its proper divisors (1).

20784989921 is an equidigital number, since it uses as much as digits as its factorization.

20784989921 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 5225472, while the sum is 59.

The spelling of 20784989921 in words is "twenty billion, seven hundred eighty-four million, nine hundred eighty-nine thousand, nine hundred twenty-one".