1211805521 has 2 divisors, whose sum is σ = 1211805522. Its totient is φ = 1211805520.

The previous prime is 1211805487. The next prime is 1211805523. The reversal of 1211805521 is 1255081121.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1124663296 + 87142225 = 33536^2 + 9335^2 .

It is a cyclic number.

It is not a de Polignac number, because 1211805521 - 2¹⁰ = 1211804497 is a prime.

Together with 1211805523, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (1211805523) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 605902760 + 605902761.

It is an arithmetic number, because the mean of its divisors is an integer number (605902761).

Almost surely, 2^1211805521 is an apocalyptic number.

It is an amenable number.

1211805521 is a deficient number, since it is larger than the sum of its proper divisors (1).

1211805521 is an equidigital number, since it uses as much as digits as its factorization.

1211805521 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 800, while the sum is 26.

The square root of 1211805521 is about 34810.9971273447. The cubic root of 1211805521 is about 1066.1319918766.

Adding to 1211805521 its reverse (1255081121), we get a palindrome (2466886642).

The spelling of 1211805521 in words is "one billion, two hundred eleven million, eight hundred five thousand, five hundred twenty-one".