21787028789 has 2 divisors, whose sum is σ = 21787028790. Its totient is φ = 21787028788.

The previous prime is 21787028773. The next prime is 21787028797. The reversal of 21787028789 is 98782078712.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12575828164 + 9211200625 = 112142^2 + 95975^2 .

It is a cyclic number.

It is not a de Polignac number, because 21787028789 - 2⁴ = 21787028773 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21787028189) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10893514394 + 10893514395.

It is an arithmetic number, because the mean of its divisors is an integer number (10893514395).

Almost surely, 2^21787028789 is an apocalyptic number.

It is an amenable number.

21787028789 is a deficient number, since it is larger than the sum of its proper divisors (1).

21787028789 is an equidigital number, since it uses as much as digits as its factorization.

21787028789 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 6322176, while the sum is 59.

The spelling of 21787028789 in words is "twenty-one billion, seven hundred eighty-seven million, twenty-eight thousand, seven hundred eighty-nine".