1221221221991 has 2 divisors, whose sum is σ = 1221221221992. Its totient is φ = 1221221221990.

The previous prime is 1221221221967. The next prime is 1221221222063. The reversal of 1221221221991 is 1991221221221.

It is a weak prime.

It is an emirp because it is prime and its reverse (1991221221221) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 1221221221991 - 2²² = 1221217027687 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1221221221291) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 610610610995 + 610610610996.

It is an arithmetic number, because the mean of its divisors is an integer number (610610610996).

Almost surely, 2^{1221221221991} is an apocalyptic number.

1221221221991 is a deficient number, since it is larger than the sum of its proper divisors (1).

1221221221991 is an equidigital number, since it uses as much as digits as its factorization.

1221221221991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 5184, while the sum is 35.

The spelling of 1221221221991 in words is "one trillion, two hundred twenty-one billion, two hundred twenty-one million, two hundred twenty-one thousand, nine hundred ninety-one".