21011020981 has 2 divisors, whose sum is σ = 21011020982. Its totient is φ = 21011020980.

The previous prime is 21011020967. The next prime is 21011021033. The reversal of 21011020981 is 18902011012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19602520081 + 1408500900 = 140009^2 + 37530^2 .

It is a cyclic number.

It is not a de Polignac number, because 21011020981 - 2⁷ = 21011020853 is a prime.

It is a super-2 number, since 2×21011020981² (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 (21311020981) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10505510490 + 10505510491.

It is an arithmetic number, because the mean of its divisors is an integer number (10505510491).

Almost surely, 2^21011020981 is an apocalyptic number.

It is an amenable number.

21011020981 is a deficient number, since it is larger than the sum of its proper divisors (1).

21011020981 is an equidigital number, since it uses as much as digits as its factorization.

21011020981 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 288, while the sum is 25.

Adding to 21011020981 its reverse (18902011012), we get a palindrome (39913031993).

The spelling of 21011020981 in words is "twenty-one billion, eleven million, twenty thousand, nine hundred eighty-one".