21855409 has 2 divisors, whose sum is σ = 21855410. Its totient is φ = 21855408.

The previous prime is 21855401. The next prime is 21855437. The reversal of 21855409 is 90455812.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15429184 + 6426225 = 3928^2 + 2535^2 .

It is a cyclic number.

It is not a de Polignac number, because 21855409 - 2³ = 21855401 is a prime.

It is not a weakly prime, because it can be changed into another prime (21855401) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10927704 + 10927705.

It is an arithmetic number, because the mean of its divisors is an integer number (10927705).

Almost surely, 2^21855409 is an apocalyptic number.

It is an amenable number.

21855409 is a deficient number, since it is larger than the sum of its proper divisors (1).

21855409 is an equidigital number, since it uses as much as digits as its factorization.

21855409 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 14400, while the sum is 34.

The square root of 21855409 is about 4674.9768983386. The cubic root of 21855409 is about 279.5887201643.

The spelling of 21855409 in words is "twenty-one million, eight hundred fifty-five thousand, four hundred nine".