1211020991 has 2 divisors, whose sum is σ = 1211020992. Its totient is φ = 1211020990.

The previous prime is 1211020981. The next prime is 1211020999. The reversal of 1211020991 is 1990201121.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 1211020991 - 2⁶ = 1211020927 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 1211020991.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1211020999) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 605510495 + 605510496.

It is an arithmetic number, because the mean of its divisors is an integer number (605510496).

Almost surely, 2^1211020991 is an apocalyptic number.

1211020991 is a deficient number, since it is larger than the sum of its proper divisors (1).

1211020991 is an equidigital number, since it uses as much as digits as its factorization.

1211020991 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 324, while the sum is 26.

The square root of 1211020991 is about 34799.7268811122. The cubic root of 1211020991 is about 1065.9018688407.

The spelling of 1211020991 in words is "one billion, two hundred eleven million, twenty thousand, nine hundred ninety-one".