20657821 has 2 divisors, whose sum is σ = 20657822. Its totient is φ = 20657820.

The previous prime is 20657801. The next prime is 20657827. The reversal of 20657821 is 12875602.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18062500 + 2595321 = 4250^2 + 1611^2 .

It is a cyclic number.

It is not a de Polignac number, because 20657821 - 2¹¹ = 20655773 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20657827) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10328910 + 10328911.

It is an arithmetic number, because the mean of its divisors is an integer number (10328911).

Almost surely, 2^20657821 is an apocalyptic number.

It is an amenable number.

20657821 is a deficient number, since it is larger than the sum of its proper divisors (1).

20657821 is an equidigital number, since it uses as much as digits as its factorization.

20657821 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 6720, while the sum is 31.

The square root of 20657821 is about 4545.0875679133. The cubic root of 20657821 is about 274.3857186778.

The spelling of 20657821 in words is "twenty million, six hundred fifty-seven thousand, eight hundred twenty-one".