• 155 can be written using four 4's:

155 has 4 divisors (see below), whose sum is σ = 192. Its totient is φ = 120.

The previous prime is 151. The next prime is 157. The reversal of 155 is 551.

155 = T_{4} + T_{5} + ... +
T_{9}.

155 is nontrivially palindromic in base 11.

155 is an esthetic number in base 4 and base 13, because in such bases its adjacent digits differ by 1.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 551 = 19 ⋅29.

It is not a de Polignac number, because 155 - 2^{2} = 151 is a prime.

It is a nude number because it is divisible by every one of its digits.

It is an Ulam number.

It is a house number.

It is a Duffinian number.

155 is an undulating number in base 11.

It is a plaindrome in base 8, base 10, base 13 and base 16.

It is a nialpdrome in base 5, base 7, base 14 and base 15.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 11 + ... + 20.

It is an arithmetic number, because the mean of its divisors is an integer number (48).

155 is a deficient number, since it is larger than the sum of its proper divisors (37).

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

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

The sum of its prime factors is 36.

The product of its digits is 25, while the sum is 11.

The square root of 155 is about 12.4498995980. The cubic root of 155 is about 5.3716853549.

Subtracting from 155 its sum of digits (11), we obtain a square (144 = 12^{2}).

The spelling of 155 in words is "one hundred fifty-five", and thus it is an aban number.

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