cp's OEIS Frontend

PARI

{a(n) = my(A); if( n<1, 0, A = vector( n*28 + 48, k, k+1); for( i = 1, 3, A = select( k -> k%prime(i), A) ); polcoeff( (1 - x) * Ser( select( k -> k>7 && (k%7) == 0, A) / 7), n)) }; /* Michael Somos, Mar 10 2014 */
(C#)
// dp(4) = GeneratePrimeDifferencialPattern( 4 );
static void GeneratePrimeDifferencialPattern( int ordinal )
{
    // Contract
    if( ordinal < 1 )
        throw new ArgumentOutOfRangeException( "ordinal" );
    // Local data
    int size = 1 << 18;
    int[] numberLine = Enumerable.Range( 2, size ).ToArray();
    int pointer = 0;
    // Apply sieve: for each integer greater than 1
    while( pointer < numberLine.Length )
    {
        // Locals
        int x = numberLine[pointer];
        int index = pointer;
        List pattern = new List();
        int skips = 0;
        int count = 0;
        bool counting = true;
        // Find all products
        for( int n = x + x; n < size; n += x )
        {
            // Fast forward through number-line
            while( numberLine[++index] < n )
                skips++;
            // If the number was not already removed
            if( numberLine[index] == n )
            {
                // Add skip count to pattern
                pattern.Add( numberLine[index] );
                // Mark as not prime
                numberLine[index] = 0;
                // Reset skips
                if( counting )
                {
                    count++;
                    if( skips <= 2 )
                        counting = false;
                }
                skips = 0;
            }
            // Otherwise we've skipped again
            else skips++;
        }
        // Reduce number-line
        numberLine = numberLine.Where( n => n > 0 ).ToArray();
        // If we have a pattern we want
        if( pattern.Any() && pointer == ordinal - 1 )
        {
            // Report pattern
            int prime = numberLine[ordinal-1];
            var d = pattern.Take( count ).ToArray();
            List dp = new List();
            for( int y = 1; y < count; y++ )
                dp.Add( ( d[y] - d[y - 1] ) / prime );
            System.Console.WriteLine( "Pattern P({0}) = {1} :: dp({0}) = {2}", pointer + 1, numberLine[pointer], String.Join( ", ", dp ) );
            return;
        }
        // Move number-line pointer forward
        pointer++;
    }
}