21113343721 has 2 divisors, whose sum is σ = 21113343722. Its totient is φ = 21113343720.

The previous prime is 21113343673. The next prime is 21113343793. The reversal of 21113343721 is 12734331112.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13750845696 + 7362498025 = 117264^2 + 85805^2 .

It is a cyclic number.

It is not a de Polignac number, because 21113343721 - 2¹⁷ = 21113212649 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21113343721.

It is not a weakly prime, because it can be changed into another prime (21113347721) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10556671860 + 10556671861.

It is an arithmetic number, because the mean of its divisors is an integer number (10556671861).

Almost surely, 2^21113343721 is an apocalyptic number.

It is an amenable number.

21113343721 is a deficient number, since it is larger than the sum of its proper divisors (1).

21113343721 is an equidigital number, since it uses as much as digits as its factorization.

21113343721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3024, while the sum is 28.

Adding to 21113343721 its reverse (12734331112), we get a palindrome (33847674833).

The spelling of 21113343721 in words is "twenty-one billion, one hundred thirteen million, three hundred forty-three thousand, seven hundred twenty-one".