21165409 has 2 divisors, whose sum is σ = 21165410. Its totient is φ = 21165408.

The previous prime is 21165383. The next prime is 21165421. The reversal of 21165409 is 90456112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20729809 + 435600 = 4553^2 + 660^2 .

It is a cyclic number.

It is not a de Polignac number, because 21165409 - 2¹¹ = 21163361 is a prime.

It is not a weakly prime, because it can be changed into another prime (21165479) by changing a digit.

It is a good prime.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10582704 + 10582705.

It is an arithmetic number, because the mean of its divisors is an integer number (10582705).

Almost surely, 2^21165409 is an apocalyptic number.

It is an amenable number.

21165409 is a deficient number, since it is larger than the sum of its proper divisors (1).

21165409 is an equidigital number, since it uses as much as digits as its factorization.

21165409 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2160, while the sum is 28.

The square root of 21165409 is about 4600.5878972149. The cubic root of 21165409 is about 276.6148905546.

The spelling of 21165409 in words is "twenty-one million, one hundred sixty-five thousand, four hundred nine".