1216655561 has 4 divisors (see below), whose sum is σ = 1327260624. Its totient is φ = 1106050500.

The previous prime is 1216655533. The next prime is 1216655569. The reversal of 1216655561 is 1655566121.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 1216655561 - 2³⁰ = 142913737 is a prime.

It is a super-2 number, since 2×1216655561² = 2960501508224449442, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1216655569) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 55302515 + ... + 55302536.

It is an arithmetic number, because the mean of its divisors is an integer number (331815156).

Almost surely, 2^1216655561 is an apocalyptic number.

1216655561 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

1216655561 is a deficient number, since it is larger than the sum of its proper divisors (110605063).

1216655561 is a wasteful number, since it uses less digits than its factorization.

1216655561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 110605062.

The product of its digits is 54000, while the sum is 38.

The square root of 1216655561 is about 34880.5900322801. The cubic root of 1216655561 is about 1067.5524342465.

The spelling of 1216655561 in words is "one billion, two hundred sixteen million, six hundred fifty-five thousand, five hundred sixty-one".