1221212001991 has 2 divisors, whose sum is σ = 1221212001992. Its totient is φ = 1221212001990.

The previous prime is 1221212001979. The next prime is 1221212002027. The reversal of 1221212001991 is 1991002121221.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 1221212001991 - 2⁵ = 1221212001959 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1221212011991) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 610606000995 + 610606000996.

It is an arithmetic number, because the mean of its divisors is an integer number (610606000996).

Almost surely, 2^{1221212001991} is an apocalyptic number.

1221212001991 is a deficient number, since it is larger than the sum of its proper divisors (1).

1221212001991 is an equidigital number, since it uses as much as digits as its factorization.

1221212001991 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1296, while the sum is 31.

The spelling of 1221212001991 in words is "one trillion, two hundred twenty-one billion, two hundred twelve million, one thousand, nine hundred ninety-one".