20666221 has 2 divisors, whose sum is σ = 20666222. Its totient is φ = 20666220.

The previous prime is 20666209. The next prime is 20666249. The reversal of 20666221 is 12266602.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 11485321 + 9180900 = 3389^2 + 3030^2 .

It is a cyclic number.

It is not a de Polignac number, because 20666221 - 2¹⁷ = 20535149 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20666201) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10333110 + 10333111.

It is an arithmetic number, because the mean of its divisors is an integer number (10333111).

Almost surely, 2^20666221 is an apocalyptic number.

It is an amenable number.

20666221 is a deficient number, since it is larger than the sum of its proper divisors (1).

20666221 is an equidigital number, since it uses as much as digits as its factorization.

20666221 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1728, while the sum is 25.

The square root of 20666221 is about 4546.0115485995. The cubic root of 20666221 is about 274.4229043956.

The spelling of 20666221 in words is "twenty million, six hundred sixty-six thousand, two hundred twenty-one".