21568920509 has 2 divisors, whose sum is σ = 21568920510. Its totient is φ = 21568920508.

The previous prime is 21568920487. The next prime is 21568920557. The reversal of 21568920509 is 90502986512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18872714884 + 2696205625 = 137378^2 + 51925^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21568920509 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21568920559) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10784460254 + 10784460255.

It is an arithmetic number, because the mean of its divisors is an integer number (10784460255).

Almost surely, 2^21568920509 is an apocalyptic number.

It is an amenable number.

21568920509 is a deficient number, since it is larger than the sum of its proper divisors (1).

21568920509 is an equidigital number, since it uses as much as digits as its factorization.

21568920509 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 388800, while the sum is 47.

The spelling of 21568920509 in words is "twenty-one billion, five hundred sixty-eight million, nine hundred twenty thousand, five hundred nine".