1221220009991 has 2 divisors, whose sum is σ = 1221220009992. Its totient is φ = 1221220009990.

The previous prime is 1221220009967. The next prime is 1221220010033. The reversal of 1221220009991 is 1999000221221.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 1221220009991 - 2¹⁴ = 1221219993607 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1221220005991) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 610610004995 + 610610004996.

It is an arithmetic number, because the mean of its divisors is an integer number (610610004996).

Almost surely, 2^{1221220009991} is an apocalyptic number.

1221220009991 is a deficient number, since it is larger than the sum of its proper divisors (1).

1221220009991 is an equidigital number, since it uses as much as digits as its factorization.

1221220009991 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 11664, while the sum is 38.

The spelling of 1221220009991 in words is "one trillion, two hundred twenty-one billion, two hundred twenty million, nine thousand, nine hundred ninety-one".