to write the program for semi , tri, quad and upto 15primes

As I'm not sure how you'd want to present the generation of these numbers in an ASP.NET application, I've used a console application instead. The basic logic will, of course, be the same:

using System;

using System.Collections.Generic;

using System.Linq;

class Test

{

static void Main()

{

int n = 5;

int limit = 180;

List nPrimes = GetN_AlmostPrimes(n, limit);

for(int i = 0; i < nPrimes.Count; i++)

{

Console.Write("{0,8}", nPrimes[i]);

}

static bool IsPrime(int i)

{

if (i < 2) return false;

for (int j = 2; j <= i / 2; j++)

{

if (i % j == 0) return false;

}

return true;

}

static List GetN_AlmostPrimes(int n, int limit)

{

List primes = new List();

int highest = limit/(1 << (n - 1));

for (int i = 2; i <= highest; i++)

{

if (IsPrime(i))

{

primes.Add(i);

}

if (n > 1)

{

IEnumerable nPrimes = primes;

for(int i = 2; i <= n; i++)

{

List tempList = new List();

foreach(int prime in primes)

{

foreach(int nPrime in nPrimes)

{

int temp = prime * nPrime;

if (temp <= limit) tempList.Add(temp);

}

nPrimes = tempList.Distinct();

}

return nPrimes.OrderBy(p => p).ToList();

}

else

{

return primes;

}

}

I've tested this for values of n from 2 (semi prime) to 5 (quint prime) and the results are consistent with those shown in the following link:

http://mathworld.wolfram.com/AlmostPrime.html

1 Reply

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Vulpes13y ago
As I'm not sure how you'd want to present the generation of these numbers in an ASP.NET application, I've used a console application instead. The basic logic will, of course, be the same:

using System;
using System.Collections.Generic;
using System.Linq;

class Test
{
static void Main()
{
int n = 5;
int limit = 180;
List nPrimes = GetN_AlmostPrimes(n, limit);

for(int i = 0; i < nPrimes.Count; i++)
{
Console.Write("{0,8}", nPrimes[i]);
}
}

static bool IsPrime(int i)
{
if (i < 2) return false;

for (int j = 2; j <= i / 2; j++)
{
if (i % j == 0) return false;
}

return true;
}

static List GetN_AlmostPrimes(int n, int limit)
{
List primes = new List();

int highest = limit/(1 << (n - 1));

for (int i = 2; i <= highest; i++)
{
if (IsPrime(i))
{
primes.Add(i);
}
}

if (n > 1)
{
IEnumerable nPrimes = primes;

for(int i = 2; i <= n; i++)
{
List tempList = new List();

foreach(int prime in primes)
{
foreach(int nPrime in nPrimes)
{
int temp = prime * nPrime;
if (temp <= limit) tempList.Add(temp);
}
}

nPrimes = tempList.Distinct();
}
return nPrimes.OrderBy(p => p).ToList();
}
else
{
return primes;
}
}
}

I've tested this for values of n from 2 (semi prime) to 5 (quint prime) and the results are consistent with those shown in the following link:

http://mathworld.wolfram.com/AlmostPrime.html