21002105309 has 2 divisors, whose sum is σ = 21002105310. Its totient is φ = 21002105308.

The previous prime is 21002105287. The next prime is 21002105321. The reversal of 21002105309 is 90350120012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19419816025 + 1582289284 = 139355^2 + 39778^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21002105309 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21002105359) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10501052654 + 10501052655.

It is an arithmetic number, because the mean of its divisors is an integer number (10501052655).

Almost surely, 2^21002105309 is an apocalyptic number.

It is an amenable number.

21002105309 is a deficient number, since it is larger than the sum of its proper divisors (1).

21002105309 is an equidigital number, since it uses as much as digits as its factorization.

21002105309 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 540, while the sum is 23.

The spelling of 21002105309 in words is "twenty-one billion, two million, one hundred five thousand, three hundred nine".