21111502721 has 2 divisors, whose sum is σ = 21111502722. Its totient is φ = 21111502720.

The previous prime is 21111502673. The next prime is 21111502759. The reversal of 21111502721 is 12720511112.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18950275600 + 2161227121 = 137660^2 + 46489^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21111502721 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (21111502781) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10555751360 + 10555751361.

It is an arithmetic number, because the mean of its divisors is an integer number (10555751361).

Almost surely, 2^21111502721 is an apocalyptic number.

It is an amenable number.

21111502721 is a deficient number, since it is larger than the sum of its proper divisors (1).

21111502721 is an equidigital number, since it uses as much as digits as its factorization.

21111502721 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 280, while the sum is 23.

The spelling of 21111502721 in words is "twenty-one billion, one hundred eleven million, five hundred two thousand, seven hundred twenty-one".