1221121991809 has 2 divisors, whose sum is σ = 1221121991810. Its totient is φ = 1221121991808.

The previous prime is 1221121991797. The next prime is 1221121991821. The reversal of 1221121991809 is 9081991211221.

It is a balanced prime because it is at equal distance from previous prime (1221121991797) and next prime (1221121991821).

It can be written as a sum of positive squares in only one way, i.e., 681404022784 + 539717969025 = 825472^2 + 734655^2 .

It is an emirp because it is prime and its reverse (9081991211221) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 1221121991809 - 2¹¹ = 1221121989761 is a prime.

It is a super-2 number, since 2×1221121991809² (a number of 25 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (1221121992809) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 610560995904 + 610560995905.

It is an arithmetic number, because the mean of its divisors is an integer number (610560995905).

Almost surely, 2^{1221121991809} is an apocalyptic number.

It is an amenable number.

1221121991809 is a deficient number, since it is larger than the sum of its proper divisors (1).

1221121991809 is an equidigital number, since it uses as much as digits as its factorization.

1221121991809 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 46656, while the sum is 46.

The spelling of 1221121991809 in words is "one trillion, two hundred twenty-one billion, one hundred twenty-one million, nine hundred ninety-one thousand, eight hundred nine".