21340409 has 2 divisors, whose sum is σ = 21340410. Its totient is φ = 21340408.

The previous prime is 21340387. The next prime is 21340411. The reversal of 21340409 is 90404312.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 10758400 + 10582009 = 3280^2 + 3253^2 .

It is a cyclic number.

It is not a de Polignac number, because 21340409 - 2¹⁶ = 21274873 is a prime.

It is a Sophie Germain prime.

Together with 21340411, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (21340469) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10670204 + 10670205.

It is an arithmetic number, because the mean of its divisors is an integer number (10670205).

Almost surely, 2^21340409 is an apocalyptic number.

It is an amenable number.

21340409 is a deficient number, since it is larger than the sum of its proper divisors (1).

21340409 is an equidigital number, since it uses as much as digits as its factorization.

21340409 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 864, while the sum is 23.

The square root of 21340409 is about 4619.5680534007. The cubic root of 21340409 is about 277.3751688088.

The spelling of 21340409 in words is "twenty-one million, three hundred forty thousand, four hundred nine".