21210110221981 has 2 divisors, whose sum is σ = 21210110221982. Its totient is φ = 21210110221980.

The previous prime is 21210110221957. The next prime is 21210110222009. The reversal of 21210110221981 is 18912201101212.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15455552136025 + 5754558085956 = 3931355^2 + 2398866^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21210110221981 is a prime.

It is a super-2 number, since 2×21210110221981² (a number of 27 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21210110221901) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10605055110990 + 10605055110991.

It is an arithmetic number, because the mean of its divisors is an integer number (10605055110991).

Almost surely, 2^{21210110221981} is an apocalyptic number.

It is an amenable number.

21210110221981 is a deficient number, since it is larger than the sum of its proper divisors (1).

21210110221981 is an equidigital number, since it uses as much as digits as its factorization.

21210110221981 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 31.

The spelling of 21210110221981 in words is "twenty-one trillion, two hundred ten billion, one hundred ten million, two hundred twenty-one thousand, nine hundred eighty-one".