21201210721 has 2 divisors, whose sum is σ = 21201210722. Its totient is φ = 21201210720.

The previous prime is 21201210707. The next prime is 21201210749. The reversal of 21201210721 is 12701210212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17852968225 + 3348242496 = 133615^2 + 57864^2 .

It is a cyclic number.

It is not a de Polignac number, because 21201210721 - 2⁵ = 21201210689 is a prime.

It is not a weakly prime, because it can be changed into another prime (21201210761) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10600605360 + 10600605361.

It is an arithmetic number, because the mean of its divisors is an integer number (10600605361).

Almost surely, 2^21201210721 is an apocalyptic number.

It is an amenable number.

21201210721 is a deficient number, since it is larger than the sum of its proper divisors (1).

21201210721 is an equidigital number, since it uses as much as digits as its factorization.

21201210721 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 112, while the sum is 19.

Adding to 21201210721 its reverse (12701210212), we get a palindrome (33902420933).

The spelling of 21201210721 in words is "twenty-one billion, two hundred one million, two hundred ten thousand, seven hundred twenty-one".