1221780991 has 8 divisors (see below), whose sum is σ = 1264410000. Its totient is φ = 1179185280.

The previous prime is 1221780977. The next prime is 1221781003. The reversal of 1221780991 is 1990871221.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 1221780991 - 2⁹ = 1221780479 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 (1221780961) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 83760 + ... + 97258.

It is an arithmetic number, because the mean of its divisors is an integer number (158051250).

Almost surely, 2^1221780991 is an apocalyptic number.

1221780991 is a deficient number, since it is larger than the sum of its proper divisors (42629009).

1221780991 is a wasteful number, since it uses less digits than its factorization.

1221780991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16649.

The product of its (nonzero) digits is 18144, while the sum is 40.

The square root of 1221780991 is about 34953.9839074175. The cubic root of 1221780991 is about 1069.0494341228.

The spelling of 1221780991 in words is "one billion, two hundred twenty-one million, seven hundred eighty thousand, nine hundred ninety-one".