21000010721 has 2 divisors, whose sum is σ = 21000010722. Its totient is φ = 21000010720.

The previous prime is 21000010649. The next prime is 21000010727. The reversal of 21000010721 is 12701000012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19450486225 + 1549524496 = 139465^2 + 39364^2 .

It is a cyclic number.

It is not a de Polignac number, because 21000010721 - 2²² = 20995816417 is a prime.

It is a super-2 number, since 2×21000010721² (a number of 21 digits) contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21000010696 and 21000010705.

It is not a weakly prime, because it can be changed into another prime (21000010727) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10500005360 + 10500005361.

It is an arithmetic number, because the mean of its divisors is an integer number (10500005361).

Almost surely, 2^21000010721 is an apocalyptic number.

It is an amenable number.

21000010721 is a deficient number, since it is larger than the sum of its proper divisors (1).

21000010721 is an equidigital number, since it uses as much as digits as its factorization.

21000010721 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 28, while the sum is 14.

Adding to 21000010721 its reverse (12701000012), we get a palindrome (33701010733).

The spelling of 21000010721 in words is "twenty-one billion, ten thousand, seven hundred twenty-one".