21613309 has 2 divisors, whose sum is σ = 21613310. Its totient is φ = 21613308.

The previous prime is 21613259. The next prime is 21613321. The reversal of 21613309 is 90331612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19554084 + 2059225 = 4422^2 + 1435^2 .

It is a cyclic number.

It is not a de Polignac number, because 21613309 - 2¹³ = 21605117 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21613349) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10806654 + 10806655.

It is an arithmetic number, because the mean of its divisors is an integer number (10806655).

Almost surely, 2^21613309 is an apocalyptic number.

It is an amenable number.

21613309 is a deficient number, since it is larger than the sum of its proper divisors (1).

21613309 is an equidigital number, since it uses as much as digits as its factorization.

21613309 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 972, while the sum is 25.

The square root of 21613309 is about 4649.0116153867. The cubic root of 21613309 is about 278.5525172598.

The spelling of 21613309 in words is "twenty-one million, six hundred thirteen thousand, three hundred nine".