Thank you Jeff for a good "filler", there are many cracks "float"ing around when it comes to math and numbers on the platform. It is also far to easy to miss the fact that float and real are Approximate-number data types, in fact not reliable after the 15th digit as this little factorial sample here shows;

/* Calculate Factorial */

/* SQL Server => 2012 */

DECLARE @TOPBIGINT= 22;

;WITH NUMBERS AS

(

SELECT

CAST(ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) AS FLOAT(53)) AS N

FROM

(VALUES (1), (1), (1), (1), (1), (1), (1), (1)) AS A(N)

,(VALUES (1), (1), (1), (1), (1), (1), (1), (1)) AS B(N)

ORDER BY 1 OFFSET 0 ROWS FETCH FIRST (@TOP) ROWS ONLY

)

,N_EXP AS

(

SELECT

ROW_NUMBER() OVER (PARTITION BY N2.N ORDER BY (SELECT NULL)) AS N_RID

,N2.N AS N

,EXP(SUM(LOG(N1.N)) OVER (PARTITION BY N2.N)) AS N_EXP

,CAST(EXP(CAST((SUM(CAST(LOG(N1.N) AS DECIMAL(38,16)))

OVER (PARTITION BY N2.N)) AS DECIMAL(38,16)))

AS DECIMAL(38,16)) AS N_DCEXP

FROM NUMBERS N1

CROSS JOIN NUMBERS N2

WHERE N1.N <= N2.N

)

SELECT

NX.N AS N

,NX.N_EXP AS NX_EXP

,CAST(NX.N_EXP AS DECIMAL(38,16)) AS NX_EXPD

,NX.N_DCEXP AS NX_DDEXP

,STR(NX.N_EXP,38,16) AS NX_STR

FROM N_EXP NX

WHERE NX.N_RID = 1;