21212020981 has 2 divisors, whose sum is σ = 21212020982. Its totient is φ = 21212020980.

The previous prime is 21212020979. The next prime is 21212020987. The reversal of 21212020981 is 18902021212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15964322500 + 5247698481 = 126350^2 + 72441^2 .

It is a cyclic number.

It is not a de Polignac number, because 21212020981 - 2¹ = 21212020979 is a prime.

It is a super-2 number, since 2×21212020981² (a number of 21 digits) contains 22 as substring.

Together with 21212020979, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21212020987) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10606010490 + 10606010491.

It is an arithmetic number, because the mean of its divisors is an integer number (10606010491).

Almost surely, 2^21212020981 is an apocalyptic number.

It is an amenable number.

21212020981 is a deficient number, since it is larger than the sum of its proper divisors (1).

21212020981 is an equidigital number, since it uses as much as digits as its factorization.

21212020981 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1152, while the sum is 28.

The spelling of 21212020981 in words is "twenty-one billion, two hundred twelve million, twenty thousand, nine hundred eighty-one".