21641309 has 2 divisors, whose sum is σ = 21641310. Its totient is φ = 21641308.

The previous prime is 21641303. The next prime is 21641311. The reversal of 21641309 is 90314612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12581209 + 9060100 = 3547^2 + 3010^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21641309 is a prime.

Together with 21641311, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21641303) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10820654 + 10820655.

It is an arithmetic number, because the mean of its divisors is an integer number (10820655).

Almost surely, 2^21641309 is an apocalyptic number.

It is an amenable number.

21641309 is a deficient number, since it is larger than the sum of its proper divisors (1).

21641309 is an equidigital number, since it uses as much as digits as its factorization.

21641309 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1296, while the sum is 26.

The square root of 21641309 is about 4652.0220334818. The cubic root of 21641309 is about 278.6727534352.

The spelling of 21641309 in words is "twenty-one million, six hundred forty-one thousand, three hundred nine".