20581721 has 2 divisors, whose sum is σ = 20581722. Its totient is φ = 20581720.

The previous prime is 20581709. The next prime is 20581777. The reversal of 20581721 is 12718502.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20430400 + 151321 = 4520^2 + 389^2 .

It is a cyclic number.

It is not a de Polignac number, because 20581721 - 2¹⁰ = 20580697 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (20589721) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10290860 + 10290861.

It is an arithmetic number, because the mean of its divisors is an integer number (10290861).

Almost surely, 2^20581721 is an apocalyptic number.

It is an amenable number.

20581721 is a deficient number, since it is larger than the sum of its proper divisors (1).

20581721 is an equidigital number, since it uses as much as digits as its factorization.

20581721 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1120, while the sum is 26.

The square root of 20581721 is about 4536.7081678239. The cubic root of 20581721 is about 274.0483735433.

The spelling of 20581721 in words is "twenty million, five hundred eighty-one thousand, seven hundred twenty-one".