21021230981 has 2 divisors, whose sum is σ = 21021230982. Its totient is φ = 21021230980.

The previous prime is 21021230939. The next prime is 21021231013. The reversal of 21021230981 is 18903212012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18929632225 + 2091598756 = 137585^2 + 45734^2 .

It is a cyclic number.

It is not a de Polignac number, because 21021230981 - 2⁶ = 21021230917 is a prime.

It is a super-2 number, since 2×21021230981² (a number of 21 digits) contains 22 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21021230911) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10510615490 + 10510615491.

It is an arithmetic number, because the mean of its divisors is an integer number (10510615491).

Almost surely, 2^21021230981 is an apocalyptic number.

It is an amenable number.

21021230981 is a deficient number, since it is larger than the sum of its proper divisors (1).

21021230981 is an equidigital number, since it uses as much as digits as its factorization.

21021230981 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1728, while the sum is 29.

Adding to 21021230981 its reverse (18903212012), we get a palindrome (39924442993).

The spelling of 21021230981 in words is "twenty-one billion, twenty-one million, two hundred thirty thousand, nine hundred eighty-one".