21003311981 has 2 divisors, whose sum is σ = 21003311982. Its totient is φ = 21003311980.

The previous prime is 21003311957. The next prime is 21003312007. The reversal of 21003311981 is 18911330012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18970654756 + 2032657225 = 137734^2 + 45085^2 .

It is a cyclic number.

It is not a de Polignac number, because 21003311981 - 2¹⁴ = 21003295597 is a prime.

It is a super-2 number, since 2×21003311981² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21603311981) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10501655990 + 10501655991.

It is an arithmetic number, because the mean of its divisors is an integer number (10501655991).

Almost surely, 2^21003311981 is an apocalyptic number.

It is an amenable number.

21003311981 is a deficient number, since it is larger than the sum of its proper divisors (1).

21003311981 is an equidigital number, since it uses as much as digits as its factorization.

21003311981 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1296, while the sum is 29.

Adding to 21003311981 its reverse (18911330012), we get a palindrome (39914641993).

The spelling of 21003311981 in words is "twenty-one billion, three million, three hundred eleven thousand, nine hundred eighty-one".