1221000999991 has 2 divisors, whose sum is σ = 1221000999992. Its totient is φ = 1221000999990.

The previous prime is 1221000999949. The next prime is 1221001000027. The reversal of 1221000999991 is 1999990001221.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 1221000999991 - 2⁹ = 1221000999479 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1221000999941) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 610500499995 + 610500499996.

It is an arithmetic number, because the mean of its divisors is an integer number (610500499996).

Almost surely, 2^{1221000999991} is an apocalyptic number.

1221000999991 is a deficient number, since it is larger than the sum of its proper divisors (1).

1221000999991 is an equidigital number, since it uses as much as digits as its factorization.

1221000999991 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 236196, while the sum is 52.

The spelling of 1221000999991 in words is "one trillion, two hundred twenty-one billion, nine hundred ninety-nine thousand, nine hundred ninety-one".