20641721 has 2 divisors, whose sum is σ = 20641722. Its totient is φ = 20641720.

The previous prime is 20641717. The next prime is 20641727. The reversal of 20641721 is 12714602.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15642025 + 4999696 = 3955^2 + 2236^2 .

It is a cyclic number.

It is not a de Polignac number, because 20641721 - 2² = 20641717 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (20641727) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10320860 + 10320861.

It is an arithmetic number, because the mean of its divisors is an integer number (10320861).

Almost surely, 2^20641721 is an apocalyptic number.

It is an amenable number.

20641721 is a deficient number, since it is larger than the sum of its proper divisors (1).

20641721 is an equidigital number, since it uses as much as digits as its factorization.

20641721 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 672, while the sum is 23.

The square root of 20641721 is about 4543.3160796933. The cubic root of 20641721 is about 274.3144178661.

The spelling of 20641721 in words is "twenty million, six hundred forty-one thousand, seven hundred twenty-one".