21405233209 has 2 divisors, whose sum is σ = 21405233210. Its totient is φ = 21405233208.

The previous prime is 21405233207. The next prime is 21405233249. The reversal of 21405233209 is 90233250412.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15285613225 + 6119619984 = 123635^2 + 78228^2 .

It is a cyclic number.

It is not a de Polignac number, because 21405233209 - 2¹ = 21405233207 is a prime.

Together with 21405233207, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (21405233207) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10702616604 + 10702616605.

It is an arithmetic number, because the mean of its divisors is an integer number (10702616605).

Almost surely, 2^21405233209 is an apocalyptic number.

It is an amenable number.

21405233209 is a deficient number, since it is larger than the sum of its proper divisors (1).

21405233209 is an equidigital number, since it uses as much as digits as its factorization.

21405233209 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 12960, while the sum is 31.

The spelling of 21405233209 in words is "twenty-one billion, four hundred five million, two hundred thirty-three thousand, two hundred nine".