1216391811 has 4 divisors (see below), whose sum is σ = 1621855752. Its totient is φ = 810927872.

The previous prime is 1216391807. The next prime is 1216391879. The reversal of 1216391811 is 1181936121.

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 1216391811 - 2² = 1216391807 is a prime.

It is not an unprimeable number, because it can be changed into a prime (1216391801) 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, 202731966 + ... + 202731971.

It is an arithmetic number, because the mean of its divisors is an integer number (405463938).

Almost surely, 2^1216391811 is an apocalyptic number.

1216391811 is a deficient number, since it is larger than the sum of its proper divisors (405463941).

1216391811 is an equidigital number, since it uses as much as digits as its factorization.

1216391811 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 405463940.

The product of its digits is 2592, while the sum is 33.

The square root of 1216391811 is about 34876.8090713586. The cubic root of 1216391811 is about 1067.4752863360.

The spelling of 1216391811 in words is "one billion, two hundred sixteen million, three hundred ninety-one thousand, eight hundred eleven".