1221221152561 has 2 divisors, whose sum is σ = 1221221152562. Its totient is φ = 1221221152560.

The previous prime is 1221221152559. The next prime is 1221221152601. The reversal of 1221221152561 is 1652511221221.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 894431713536 + 326789439025 = 945744^2 + 571655^2 .

It is a cyclic number.

It is not a de Polignac number, because 1221221152561 - 2¹ = 1221221152559 is a prime.

It is a super-2 number, since 2×1221221152561² (a number of 25 digits) contains 22 as substring.

Together with 1221221152559, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (1221221152531) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 610610576280 + 610610576281.

It is an arithmetic number, because the mean of its divisors is an integer number (610610576281).

Almost surely, 2^{1221221152561} is an apocalyptic number.

It is an amenable number.

1221221152561 is a deficient number, since it is larger than the sum of its proper divisors (1).

1221221152561 is an equidigital number, since it uses as much as digits as its factorization.

1221221152561 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 4800, while the sum is 31.

Adding to 1221221152561 its reverse (1652511221221), we get a palindrome (2873732373782).

The spelling of 1221221152561 in words is "one trillion, two hundred twenty-one billion, two hundred twenty-one million, one hundred fifty-two thousand, five hundred sixty-one".