21560009 has 2 divisors, whose sum is σ = 21560010. Its totient is φ = 21560008.

The previous prime is 21559999. The next prime is 21560017. The reversal of 21560009 is 90006512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19009600 + 2550409 = 4360^2 + 1597^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21560009 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (21560059) 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, 10780004 + 10780005.

It is an arithmetic number, because the mean of its divisors is an integer number (10780005).

Almost surely, 2^21560009 is an apocalyptic number.

It is an amenable number.

21560009 is a deficient number, since it is larger than the sum of its proper divisors (1).

21560009 is an equidigital number, since it uses as much as digits as its factorization.

21560009 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 540, while the sum is 23.

The square root of 21560009 is about 4643.2756756411. The cubic root of 21560009 is about 278.3233518199.

The spelling of 21560009 in words is "twenty-one million, five hundred sixty thousand, nine".