20856709 has 2 divisors, whose sum is σ = 20856710. Its totient is φ = 20856708.

The previous prime is 20856679. The next prime is 20856721. The reversal of 20856709 is 90765802.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18515809 + 2340900 = 4303^2 + 1530^2 .

It is a cyclic number.

It is not a de Polignac number, because 20856709 - 2²³ = 12468101 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20836709) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10428354 + 10428355.

It is an arithmetic number, because the mean of its divisors is an integer number (10428355).

Almost surely, 2^20856709 is an apocalyptic number.

It is an amenable number.

20856709 is a deficient number, since it is larger than the sum of its proper divisors (1).

20856709 is an equidigital number, since it uses as much as digits as its factorization.

20856709 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 30240, while the sum is 37.

The square root of 20856709 is about 4566.9146039750. The cubic root of 20856709 is about 275.2634786089.

The spelling of 20856709 in words is "twenty million, eight hundred fifty-six thousand, seven hundred nine".