1216881821 has 2 divisors, whose sum is σ = 1216881822. Its totient is φ = 1216881820.

The previous prime is 1216881773. The next prime is 1216881829. The reversal of 1216881821 is 1281886121.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1112556025 + 104325796 = 33355^2 + 10214^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1216881821 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1216881829) 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 as a sum of consecutive naturals, namely, 608440910 + 608440911.

It is an arithmetic number, because the mean of its divisors is an integer number (608440911).

Almost surely, 2^1216881821 is an apocalyptic number.

It is an amenable number.

1216881821 is a deficient number, since it is larger than the sum of its proper divisors (1).

1216881821 is an equidigital number, since it uses as much as digits as its factorization.

1216881821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 12288, while the sum is 38.

The square root of 1216881821 is about 34883.8332326022. The cubic root of 1216881821 is about 1067.6186073004.

The spelling of 1216881821 in words is "one billion, two hundred sixteen million, eight hundred eighty-one thousand, eight hundred twenty-one".