21308917909 has 2 divisors, whose sum is σ = 21308917910. Its totient is φ = 21308917908.

The previous prime is 21308917891. The next prime is 21308917913. The reversal of 21308917909 is 90971980312.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 11342889009 + 9966028900 = 106503^2 + 99830^2 .

It is a cyclic number.

It is not a de Polignac number, because 21308917909 - 2²³ = 21300529301 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21308917969) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10654458954 + 10654458955.

It is an arithmetic number, because the mean of its divisors is an integer number (10654458955).

Almost surely, 2^21308917909 is an apocalyptic number.

It is an amenable number.

21308917909 is a deficient number, since it is larger than the sum of its proper divisors (1).

21308917909 is an equidigital number, since it uses as much as digits as its factorization.

21308917909 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 244944, while the sum is 49.

The spelling of 21308917909 in words is "twenty-one billion, three hundred eight million, nine hundred seventeen thousand, nine hundred nine".