155 (one hundred
ndfifty-five) is the
natural number
In mathematics, the natural numbers are the numbers 0, 1, 2, 3, and so on, possibly excluding 0. Some start counting with 0, defining the natural numbers as the non-negative integers , while others start with 1, defining them as the positive in ...
following
154 and preceding
156.
In mathematics
143 is:
*a
composite number
A composite number is a positive integer that can be formed by multiplying two smaller positive integers. Accordingly it is a positive integer that has at least one divisor other than 1 and itself. Every positive integer is composite, prime numb ...
*a
semiprime
In mathematics, a semiprime is a natural number that is the product of exactly two prime numbers. The two primes in the product may equal each other, so the semiprimes include the squares of prime numbers.
Because there are infinitely many prime n ...
.
*a
deficient number
In number theory, a deficient number or defective number is a positive integer for which the sum of divisors of is less than . Equivalently, it is a number for which the sum of proper divisors (or aliquot sum) is less than . For example, th ...
, since
1+
5+
31=
37<155.
*
odious, since its
binary expansion
A binary number is a number expressed in the base-2 numeral system or binary numeral system, a method for representing numbers that uses only two symbols for the natural numbers: typically "0" ( zero) and "1" ( one). A ''binary number'' may als ...
has a total of 5 ones in it.
*Its prime factorization is 5*31, and the sum of the prime numbers between 5 and 31, inclusively, is 155.
There are 143 primitive
permutation group
In mathematics, a permutation group is a group ''G'' whose elements are permutations of a given set ''M'' and whose group operation is the composition of permutations in ''G'' (which are thought of as bijective functions from the set ''M'' to ...
s of degree 81.
If one adds up all the primes from the least through the greatest prime factors of 143, that is, 5 and 31, the result is 143. Only three other "small" semiprimes (10, 39, and 371) share this attribute.
References
External links
{{DEFAULTSORT:155 (Number)
Integers