20666021 has 2 divisors, whose sum is σ = 20666022. Its totient is φ = 20666020.

The previous prime is 20666003. The next prime is 20666047. The reversal of 20666021 is 12066602.

20666021 = 3214² + 3215².

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 10336225 + 10329796 = 3215^2 + 3214^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20666021 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20666221) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10333010 + 10333011.

It is an arithmetic number, because the mean of its divisors is an integer number (10333011).

Almost surely, 2^20666021 is an apocalyptic number.

20666021 is the 3215-th centered square number.

It is an amenable number.

20666021 is a deficient number, since it is larger than the sum of its proper divisors (1).

20666021 is an equidigital number, since it uses as much as digits as its factorization.

20666021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 864, while the sum is 23.

The square root of 20666021 is about 4545.9895512418. The cubic root of 20666021 is about 274.4220191384.

The spelling of 20666021 in words is "twenty million, six hundred sixty-six thousand, twenty-one".