20101720721 has 2 divisors, whose sum is σ = 20101720722. Its totient is φ = 20101720720.

The previous prime is 20101720687. The next prime is 20101720733. The reversal of 20101720721 is 12702710102.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15164691025 + 4937029696 = 123145^2 + 70264^2 .

It is a cyclic number.

It is not a de Polignac number, because 20101720721 - 2¹⁸ = 20101458577 is a prime.

It is not a weakly prime, because it can be changed into another prime (20101720621) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10050860360 + 10050860361.

It is an arithmetic number, because the mean of its divisors is an integer number (10050860361).

Almost surely, 2^20101720721 is an apocalyptic number.

It is an amenable number.

20101720721 is a deficient number, since it is larger than the sum of its proper divisors (1).

20101720721 is an equidigital number, since it uses as much as digits as its factorization.

20101720721 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 392, while the sum is 23.

The spelling of 20101720721 in words is "twenty billion, one hundred one million, seven hundred twenty thousand, seven hundred twenty-one".