3981816121 has 2 divisors, whose sum is σ = 3981816122. Its totient is φ = 3981816120.

The previous prime is 3981816061. The next prime is 3981816197. The reversal of 3981816121 is 1216181893.

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., 2444313600 + 1537502521 = 49440^2 + 39211^2 .

It is a cyclic number.

It is not a de Polignac number, because 3981816121 - 2⁷ = 3981815993 is a prime.

It is not a weakly prime, because it can be changed into another prime (3981816521) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1990908060 + 1990908061.

It is an arithmetic number, because the mean of its divisors is an integer number (1990908061).

Almost surely, 2^3981816121 is an apocalyptic number.

It is an amenable number.

3981816121 is a deficient number, since it is larger than the sum of its proper divisors (1).

3981816121 is an equidigital number, since it uses as much as digits as its factorization.

3981816121 is an evil number, because the sum of its binary digits is even.

The product of its digits is 20736, while the sum is 40.

The square root of 3981816121 is about 63101.6332672935. The cubic root of 3981816121 is about 1584.9919720160.

The spelling of 3981816121 in words is "three billion, nine hundred eighty-one million, eight hundred sixteen thousand, one hundred twenty-one".