1221221999 has 2 divisors, whose sum is σ = 1221222000. Its totient is φ = 1221221998.

The previous prime is 1221221993. The next prime is 1221222001. The reversal of 1221221999 is 9991221221.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 1221221999 - 2⁴ = 1221221983 is a prime.

Together with 1221222001, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1221221993) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 610610999 + 610611000.

It is an arithmetic number, because the mean of its divisors is an integer number (610611000).

Almost surely, 2^1221221999 is an apocalyptic number.

1221221999 is a deficient number, since it is larger than the sum of its proper divisors (1).

1221221999 is an equidigital number, since it uses as much as digits as its factorization.

1221221999 is an odious number, because the sum of its binary digits is odd.

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

The square root of 1221221999 is about 34945.9868797549. The cubic root of 1221221999 is about 1068.8863712810.

The spelling of 1221221999 in words is "one billion, two hundred twenty-one million, two hundred twenty-one thousand, nine hundred ninety-nine".