1221165554981 has 2 divisors, whose sum is σ = 1221165554982. Its totient is φ = 1221165554980.

The previous prime is 1221165554927. The next prime is 1221165555007. The reversal of 1221165554981 is 1894555611221.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1089299253025 + 131866301956 = 1043695^2 + 363134^2 .

It is a cyclic number.

It is not a de Polignac number, because 1221165554981 - 2²² = 1221161360677 is a prime.

It is a super-2 number, since 2×1221165554981² (a number of 25 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1221165554911) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 610582777490 + 610582777491.

It is an arithmetic number, because the mean of its divisors is an integer number (610582777491).

Almost surely, 2^{1221165554981} is an apocalyptic number.

It is an amenable number.

1221165554981 is a deficient number, since it is larger than the sum of its proper divisors (1).

1221165554981 is an equidigital number, since it uses as much as digits as its factorization.

1221165554981 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 864000, while the sum is 50.

The spelling of 1221165554981 in words is "one trillion, two hundred twenty-one billion, one hundred sixty-five million, five hundred fifty-four thousand, nine hundred eighty-one".