21016309 has 2 divisors, whose sum is σ = 21016310. Its totient is φ = 21016308.

The previous prime is 21016297. The next prime is 21016381. The reversal of 21016309 is 90361012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18922500 + 2093809 = 4350^2 + 1447^2 .

It is a cyclic number.

It is not a de Polignac number, because 21016309 - 2⁵ = 21016277 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is equal to p_1330942 and since 21016309 and 1330942 have the same sum of digits, it is a Honaker prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21016309.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21016409) 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, 10508154 + 10508155.

It is an arithmetic number, because the mean of its divisors is an integer number (10508155).

Almost surely, 2^21016309 is an apocalyptic number.

It is an amenable number.

21016309 is a deficient number, since it is larger than the sum of its proper divisors (1).

21016309 is an equidigital number, since it uses as much as digits as its factorization.

21016309 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 324, while the sum is 22.

The square root of 21016309 is about 4584.3548073857. The cubic root of 21016309 is about 275.9638202593.

The spelling of 21016309 in words is "twenty-one million, sixteen thousand, three hundred nine".