30811981 has 2 divisors, whose sum is σ = 30811982. Its totient is φ = 30811980.

The previous prime is 30811943. The next prime is 30811993. The reversal of 30811981 is 18911803.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15920100 + 14891881 = 3990^2 + 3859^2 .

It is a cyclic number.

It is not a de Polignac number, because 30811981 - 2⁷ = 30811853 is a prime.

It is a super-2 number, since 2×30811981² = 1898756346288722, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (30811381) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 15405990 + 15405991.

It is an arithmetic number, because the mean of its divisors is an integer number (15405991).

Almost surely, 2^30811981 is an apocalyptic number.

It is an amenable number.

30811981 is a deficient number, since it is larger than the sum of its proper divisors (1).

30811981 is an equidigital number, since it uses as much as digits as its factorization.

30811981 is an evil number, because the sum of its binary digits is even.

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

The square root of 30811981 is about 5550.8540784279. The cubic root of 30811981 is about 313.5016809490.

The spelling of 30811981 in words is "thirty million, eight hundred eleven thousand, nine hundred eighty-one".