1221345555891 has 8 divisors (see below), whose sum is σ = 1628596077264. Its totient is φ = 814162702560.

The previous prime is 1221345555869. The next prime is 1221345555919. The reversal of 1221345555891 is 1985555431221.

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

It is not a de Polignac number, because 1221345555891 - 2¹⁴ = 1221345539507 is a prime.

It is a Smith number, since the sum of its digits (51) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is not an unprimeable number, because it can be changed into a prime (1221345555821) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 16874880 + ... + 16947101.

It is an arithmetic number, because the mean of its divisors is an integer number (203574509658).

Almost surely, 2^{1221345555891} is an apocalyptic number.

1221345555891 is a deficient number, since it is larger than the sum of its proper divisors (407250521373).

1221345555891 is a wasteful number, since it uses less digits than its factorization.

1221345555891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 33834021.

The product of its digits is 2160000, while the sum is 51.

The spelling of 1221345555891 in words is "one trillion, two hundred twenty-one billion, three hundred forty-five million, five hundred fifty-five thousand, eight hundred ninety-one".