1211111981 has 2 divisors, whose sum is σ = 1211111982. Its totient is φ = 1211111980.

The previous prime is 1211111963. The next prime is 1211112017. The reversal of 1211111981 is 1891111121.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 668687881 + 542424100 = 25859^2 + 23290^2 .

It is a cyclic number.

It is not a de Polignac number, because 1211111981 - 2³⁰ = 137370157 is a prime.

It is a super-2 number, since 2×1211111981² = 2933584461043488722, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 1211111981.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1211111081) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 605555990 + 605555991.

It is an arithmetic number, because the mean of its divisors is an integer number (605555991).

Almost surely, 2^1211111981 is an apocalyptic number.

It is an amenable number.

1211111981 is a deficient number, since it is larger than the sum of its proper divisors (1).

1211111981 is an equidigital number, since it uses as much as digits as its factorization.

1211111981 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 144, while the sum is 26.

The square root of 1211111981 is about 34801.0341944029. The cubic root of 1211111981 is about 1065.9285636662.

The spelling of 1211111981 in words is "one billion, two hundred eleven million, one hundred eleven thousand, nine hundred eighty-one".