1216521306 has 192 divisors, whose sum is σ = 3577706496. Its totient is φ = 288489600.

The previous prime is 1216521301. The next prime is 1216521307. The reversal of 1216521306 is 6031256121.

1216521306 is a `hidden beast` number, since 1 + 2 + 1 + 652 + 1 + 3 + 0 + 6 = 666.

It is a self number, because there is not a number n which added to its sum of digits gives 1216521306.

It is not an unprimeable number, because it can be changed into a prime (1216521301) 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 95 ways as a sum of consecutive naturals, for example, 1927611 + ... + 1928241.

It is an arithmetic number, because the mean of its divisors is an integer number (18633888).

Almost surely, 2^1216521306 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 1216521306, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1788853248).

1216521306 is an abundant number, since it is smaller than the sum of its proper divisors (2361185190).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

1216521306 is a wasteful number, since it uses less digits than its factorization.

1216521306 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 777 (or 774 counting only the distinct ones).

The product of its (nonzero) digits is 2160, while the sum is 27.

The square root of 1216521306 is about 34878.6654847917. The cubic root of 1216521306 is about 1067.5131655253.

Adding to 1216521306 its reverse (6031256121), we get a palindrome (7247777427).

The spelling of 1216521306 in words is "one billion, two hundred sixteen million, five hundred twenty-one thousand, three hundred six".