21355409 has 2 divisors, whose sum is σ = 21355410. Its totient is φ = 21355408.

The previous prime is 21355403. The next prime is 21355447. The reversal of 21355409 is 90455312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16581184 + 4774225 = 4072^2 + 2185^2 .

It is a cyclic number.

It is not a de Polignac number, because 21355409 - 2⁴ = 21355393 is a prime.

It is not a weakly prime, because it can be changed into another prime (21355403) 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, 10677704 + 10677705.

It is an arithmetic number, because the mean of its divisors is an integer number (10677705).

Almost surely, 2^21355409 is an apocalyptic number.

It is an amenable number.

21355409 is a deficient number, since it is larger than the sum of its proper divisors (1).

21355409 is an equidigital number, since it uses as much as digits as its factorization.

21355409 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 5400, while the sum is 29.

The square root of 21355409 is about 4621.1912966247. The cubic root of 21355409 is about 277.4401418386.

The spelling of 21355409 in words is "twenty-one million, three hundred fifty-five thousand, four hundred nine".