21131968789 has 2 divisors, whose sum is σ = 21131968790. Its totient is φ = 21131968788.

The previous prime is 21131968783. The next prime is 21131968909. The reversal of 21131968789 is 98786913112.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18654915889 + 2477052900 = 136583^2 + 49770^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21131968789 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21131968783) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10565984394 + 10565984395.

It is an arithmetic number, because the mean of its divisors is an integer number (10565984395).

Almost surely, 2^21131968789 is an apocalyptic number.

It is an amenable number.

21131968789 is a deficient number, since it is larger than the sum of its proper divisors (1).

21131968789 is an equidigital number, since it uses as much as digits as its factorization.

21131968789 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1306368, while the sum is 55.

The spelling of 21131968789 in words is "twenty-one billion, one hundred thirty-one million, nine hundred sixty-eight thousand, seven hundred eighty-nine".