21307109 has 2 divisors, whose sum is σ = 21307110. Its totient is φ = 21307108.

The previous prime is 21307093. The next prime is 21307123. The reversal of 21307109 is 90170312.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19624900 + 1682209 = 4430^2 + 1297^2 .

It is a cyclic number.

It is not a de Polignac number, because 21307109 - 2⁴ = 21307093 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is equal to p_1348160 and since 21307109 and 1348160 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21307609) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10653554 + 10653555.

It is an arithmetic number, because the mean of its divisors is an integer number (10653555).

Almost surely, 2^21307109 is an apocalyptic number.

It is an amenable number.

21307109 is a deficient number, since it is larger than the sum of its proper divisors (1).

21307109 is an equidigital number, since it uses as much as digits as its factorization.

21307109 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 378, while the sum is 23.

The square root of 21307109 is about 4615.9624131919. The cubic root of 21307109 is about 277.2308197851.

The spelling of 21307109 in words is "twenty-one million, three hundred seven thousand, one hundred nine".