216121981 has 2 divisors, whose sum is σ = 216121982. Its totient is φ = 216121980.

The previous prime is 216121937. The next prime is 216122033. The reversal of 216121981 is 189121612.

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., 136305625 + 79816356 = 11675^2 + 8934^2 .

It is a cyclic number.

It is not a de Polignac number, because 216121981 - 2⁷ = 216121853 is a prime.

It is a super-2 number, since 2×216121981² = 93417421342728722, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (216121931) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 108060990 + 108060991.

It is an arithmetic number, because the mean of its divisors is an integer number (108060991).

Almost surely, 2^216121981 is an apocalyptic number.

It is an amenable number.

216121981 is a deficient number, since it is larger than the sum of its proper divisors (1).

216121981 is an equidigital number, since it uses as much as digits as its factorization.

216121981 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1728, while the sum is 31.

The square root of 216121981 is about 14701.0877488708. The cubic root of 216121981 is about 600.1129241159.

It can be divided in two parts, 2161 and 21981, that added together give a palindrome (24142).

The spelling of 216121981 in words is "two hundred sixteen million, one hundred twenty-one thousand, nine hundred eighty-one".