155361221 has 2 divisors, whose sum is σ = 155361222. Its totient is φ = 155361220.

The previous prime is 155361211. The next prime is 155361223. The reversal of 155361221 is 122163551.

155361221 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 87628321 + 67732900 = 9361^2 + 8230^2 .

It is an emirp because it is prime and its reverse (122163551) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 155361221 - 2¹⁴ = 155344837 is a prime.

It is a super-3 number, since 3×155361221³ (a number of 26 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

Together with 155361223, 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 (155361223) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 77680610 + 77680611.

It is an arithmetic number, because the mean of its divisors is an integer number (77680611).

Almost surely, 2^155361221 is an apocalyptic number.

It is an amenable number.

155361221 is a deficient number, since it is larger than the sum of its proper divisors (1).

155361221 is an equidigital number, since it uses as much as digits as its factorization.

155361221 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1800, while the sum is 26.

The square root of 155361221 is about 12464.3981403034. The cubic root of 155361221 is about 537.5854946753.

The spelling of 155361221 in words is "one hundred fifty-five million, three hundred sixty-one thousand, two hundred twenty-one".