21559709 has 2 divisors, whose sum is σ = 21559710. Its totient is φ = 21559708.

The previous prime is 21559697. The next prime is 21559739. The reversal of 21559709 is 90795512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21187609 + 372100 = 4603^2 + 610^2 .

It is a cyclic number.

It is not a de Polignac number, because 21559709 - 2⁴ = 21559693 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21559739) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10779854 + 10779855.

It is an arithmetic number, because the mean of its divisors is an integer number (10779855).

Almost surely, 2^21559709 is an apocalyptic number.

It is an amenable number.

21559709 is a deficient number, since it is larger than the sum of its proper divisors (1).

21559709 is an equidigital number, since it uses as much as digits as its factorization.

21559709 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 28350, while the sum is 38.

The square root of 21559709 is about 4643.2433707485. The cubic root of 21559709 is about 278.3220608898.

The spelling of 21559709 in words is "twenty-one million, five hundred fifty-nine thousand, seven hundred nine".