21105505609 has 2 divisors, whose sum is σ = 21105505610. Its totient is φ = 21105505608.

The previous prime is 21105505607. The next prime is 21105505637. The reversal of 21105505609 is 90650550112.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16603095609 + 4502410000 = 128853^2 + 67100^2 .

It is a cyclic number.

It is not a de Polignac number, because 21105505609 - 2¹ = 21105505607 is a prime.

Together with 21105505607, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (21105505607) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10552752804 + 10552752805.

It is an arithmetic number, because the mean of its divisors is an integer number (10552752805).

Almost surely, 2^21105505609 is an apocalyptic number.

It is an amenable number.

21105505609 is a deficient number, since it is larger than the sum of its proper divisors (1).

21105505609 is an equidigital number, since it uses as much as digits as its factorization.

21105505609 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 13500, while the sum is 34.

The spelling of 21105505609 in words is "twenty-one billion, one hundred five million, five hundred five thousand, six hundred nine".