155520221 has 2 divisors, whose sum is σ = 155520222. Its totient is φ = 155520220.

The previous prime is 155520203. The next prime is 155520223. The reversal of 155520221 is 122025551.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 155500900 + 19321 = 12470^2 + 139^2 .

It is an emirp because it is prime and its reverse (122025551) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 155520221 - 2²⁶ = 88411357 is a prime.

Together with 155520223, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (155520223) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 77760110 + 77760111.

It is an arithmetic number, because the mean of its divisors is an integer number (77760111).

Almost surely, 2^155520221 is an apocalyptic number.

It is an amenable number.

155520221 is a deficient number, since it is larger than the sum of its proper divisors (1).

155520221 is an equidigital number, since it uses as much as digits as its factorization.

155520221 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1000, while the sum is 23.

The square root of 155520221 is about 12470.7746752156. The cubic root of 155520221 is about 537.7688243168.

Adding to 155520221 its reverse (122025551), we get a palindrome (277545772).

The spelling of 155520221 in words is "one hundred fifty-five million, five hundred twenty thousand, two hundred twenty-one".