210121981 has 2 divisors, whose sum is σ = 210121982. Its totient is φ = 210121980.

The previous prime is 210121979. The next prime is 210122021. The reversal of 210121981 is 189121012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 126765081 + 83356900 = 11259^2 + 9130^2 .

It is a cyclic number.

It is not a de Polignac number, because 210121981 - 2¹ = 210121979 is a prime.

It is a super-2 number, since 2×210121981² = 88302493798728722, which contains 22 as substring.

Together with 210121979, 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 (210121481) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 105060990 + 105060991.

It is an arithmetic number, because the mean of its divisors is an integer number (105060991).

Almost surely, 2^210121981 is an apocalyptic number.

It is an amenable number.

210121981 is a deficient number, since it is larger than the sum of its proper divisors (1).

210121981 is an equidigital number, since it uses as much as digits as its factorization.

210121981 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.

The square root of 210121981 is about 14495.5848795418. The cubic root of 210121981 is about 594.5072595946.

Adding to 210121981 its reverse (189121012), we get a palindrome (399242993).

The spelling of 210121981 in words is "two hundred ten million, one hundred twenty-one thousand, nine hundred eighty-one".