1211561864021 has 2 divisors, whose sum is σ = 1211561864022. Its totient is φ = 1211561864020.

The previous prime is 1211561864003. The next prime is 1211561864041. The reversal of 1211561864021 is 1204681651121.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 869535735121 + 342026128900 = 932489^2 + 584830^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1211561864021 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1211561864041) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 605780932010 + 605780932011.

It is an arithmetic number, because the mean of its divisors is an integer number (605780932011).

Almost surely, 2^{1211561864021} is an apocalyptic number.

It is an amenable number.

1211561864021 is a deficient number, since it is larger than the sum of its proper divisors (1).

1211561864021 is an equidigital number, since it uses as much as digits as its factorization.

1211561864021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 23040, while the sum is 38.

The spelling of 1211561864021 in words is "one trillion, two hundred eleven billion, five hundred sixty-one million, eight hundred sixty-four thousand, twenty-one".