1221320999 has 4 divisors (see below), whose sum is σ = 1274421936. Its totient is φ = 1168220064.

The previous prime is 1221320951. The next prime is 1221321001. The reversal of 1221320999 is 9990231221.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 1221320999 - 2¹⁶ = 1221255463 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1221320929) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 26550434 + ... + 26550479.

It is an arithmetic number, because the mean of its divisors is an integer number (318605484).

Almost surely, 2^1221320999 is an apocalyptic number.

1221320999 is a deficient number, since it is larger than the sum of its proper divisors (53100937).

1221320999 is an equidigital number, since it uses as much as digits as its factorization.

1221320999 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 53100936.

The product of its (nonzero) digits is 17496, while the sum is 38.

The square root of 1221320999 is about 34947.4033227077. The cubic root of 1221320999 is about 1068.9152540698.

The spelling of 1221320999 in words is "one billion, two hundred twenty-one million, three hundred twenty thousand, nine hundred ninety-nine".