1221111001991 has 2 divisors, whose sum is σ = 1221111001992. Its totient is φ = 1221111001990.

The previous prime is 1221111001933. The next prime is 1221111002021. The reversal of 1221111001991 is 1991001111221.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 1221111001991 - 2⁶ = 1221111001927 is a prime.

It is a super-2 number, since 2×1221111001991² (a number of 25 digits) contains 22 as substring.

It is a Sophie Germain prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1221111001931) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 610555500995 + 610555500996.

It is an arithmetic number, because the mean of its divisors is an integer number (610555500996).

Almost surely, 2^{1221111001991} is an apocalyptic number.

1221111001991 is a deficient number, since it is larger than the sum of its proper divisors (1).

1221111001991 is an equidigital number, since it uses as much as digits as its factorization.

1221111001991 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 29.

The spelling of 1221111001991 in words is "one trillion, two hundred twenty-one billion, one hundred eleven million, one thousand, nine hundred ninety-one".