DROP TABLE #Numbers
SELECT TOP 1000000 --000 
	n = ROW_NUMBER() OVER (ORDER BY a.name),
	CalcValue = CAST(NULL AS BIGINT)
INTO #Numbers
FROM master.dbo.syscolumns a, master.dbo.syscolumns b
CREATE UNIQUE CLUSTERED INDEX CIn ON #Numbers ([n] ASC) 
-- (1,000,000 row(s) affected)

SET STATISTICS IO ON
SET STATISTICS TIME ON

-- 'Quirky' update
DECLARE @Lastval INT = 0, @CalcValue BIGINT
UPDATE #Numbers SET
	@CalcValue = CalcValue = (@Lastval + n),
	@Lastval = n
-- (1,000,000 row(s) affected) / CPU time = 2968 ms,  elapsed time = 3079 ms.
-- Table #Numbers... Scan count 1, logical reads 3113, physical reads 6, read-ahead reads 3146, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

-- Recursive CTE
;WITH Calculator (n, CalcValue) AS (
	SELECT n.n, CalcValue = CAST(n.n AS BIGINT)
	FROM #Numbers n
	WHERE n.n = 1
	UNION ALL
	SELECT n.n, CalcValue = n.n + c.n
	FROM #Numbers n
	INNER JOIN Calculator c ON n.n = c.n + 1 -- nice  
	--INNER JOIN Calculator c ON c.n + 1 = n.n -- nice  
	--INNER JOIN Calculator c ON c.n = n.n - 1 -- slow 
	--INNER JOIN Calculator c ON n.n - c.n = 1 -- slow  
	--INNER JOIN Calculator c ON c.n - n.n = -1 -- slow  
)
SELECT n, CalcValue 
FROM Calculator
OPTION (MAXRECURSION 0)
-- (1,000,000 row(s) affected) / CPU time = 33297 ms,  elapsed time = 36161 ms.
-- Table 'Worktable'. Scan count 2, logical reads 6000001, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

SET STATISTICS IO Off
SET STATISTICS TIME Off