1221001211981 has 2 divisors, whose sum is σ = 1221001211982. Its totient is φ = 1221001211980.

The previous prime is 1221001211933. The next prime is 1221001212031. The reversal of 1221001211981 is 1891121001221.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1213597469956 + 7403742025 = 1101634^2 + 86045^2 .

It is a cyclic number.

It is not a de Polignac number, because 1221001211981 - 2²⁶ = 1220934103117 is a prime.

It is a super-2 number, since 2×1221001211981² (a number of 25 digits) contains 22 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1221001211081) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 610500605990 + 610500605991.

It is an arithmetic number, because the mean of its divisors is an integer number (610500605991).

Almost surely, 2^{1221001211981} is an apocalyptic number.

It is an amenable number.

1221001211981 is a deficient number, since it is larger than the sum of its proper divisors (1).

1221001211981 is an equidigital number, since it uses as much as digits as its factorization.

1221001211981 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 576, while the sum is 29.

The spelling of 1221001211981 in words is "one trillion, two hundred twenty-one billion, one million, two hundred eleven thousand, nine hundred eighty-one".