How to select only armstrong numbers from the list? - sql

Question

I want is to select Armstrong numbers from the list below list I have searched of solution of this question bu unable to find in SQL-Server:
Numbers
121
113
423
153
541
371
I am sure most of you know what's the Armstrong number and how to calculate though I am describing is for the simplicity : sum of the cubes of its digits is equal to the number itself i.e.
1*1*1 + 5*5*5 + 3*3*3 = 153
3*3*3 + 7*7*7 + 1*1*1 = 371
Please help me on this as I am also trying but seeking for quick solution. It will be very helpful to me. Thanks in advance.

Answer 1

Obviously static processing during each query is not correct approach but we can create function like this and
create function dbo.IsArmstrongNumber(#n int)
returns int as
begin
declare #retValue int = 0
declare #sum int = 0
declare #num int = #n
while #num > 0
begin
set #sum += (#num%10) * (#num%10) * (#num%10)
set #num = #num/10
end
IF #sum = #n
set #retValue = 1
return #retValue
end
Pre-processing and selecting in IN clause is better
select * from #Numbers where dbo.IsArmstrongNumber(n) = 1

Answer 2

select 153 x into #temp;
insert #temp values(371);
insert #temp values(541);
with cte as (select x, substring(cast(x as nvarchar(40)) ,1,1) as u, 1 as N FROM #temp
union all
select x, substring(cast(x as nvarchar(40)),n+1,1) as u , n+1 from cte where len(cast(x as nvarchar(40))) > n
)
select x from cte group by x having SUM(POWER(cast(u as int),3)) = x
drop table #temp;
here is the mark 2 - you can change the #ORDER to explore power of 4,5 etc
declare #order int = 3;
declare #limit int = 50000;
with nos as (select 1 no
union all
select no + 1 from nos where no < #limit),
cte as (select no as x, substring(cast(no as nvarchar(40)) ,1,1) as u, 1 as N FROM nos
union all
select x, substring(cast(x as nvarchar(40)),n+1,1) as u , n+1 from cte where len(cast(x as nvarchar(40))) > n
)
select x from cte group by x having SUM(POWER(cast(u as int),#order)) = x
option (maxrecursion 0);

Answer 3

This is a quick mod to my sum of digits UDF
Declare #Table table (Numbers int)
Insert into #Table values
(121),
(113),
(423),
(153),
(541),
(371)
Select * from #Table where [dbo].[udf-Stat-Is-Armstrong](Numbers)=1
Returns
Numbers
153
371
The UDF
CREATE Function [dbo].[udf-Stat-Is-Armstrong](#Val bigint)
Returns Bit
As
Begin
Declare #RetVal as bigint
Declare #LenInp as bigint = len(cast(#Val as varchar(25)))
;with i AS (
Select #Val / 10 n, #Val % 10 d
Union ALL
Select n / 10, n % 10
From i
Where n > 0
)
Select #RetVal = IIF(SUM(power(d,#LenInp))=#Val,1,0) FROM i;
Return #RetVal
End

Answer 4

You can use the following to find Armstrong numbers using Sql functions:
WITH Numbers AS(
SELECT 0 AS number UNION ALL SELECT number + 1 FROM Numbers WHERE number < 10000)
SELECT number AS ArmstrongNumber FROM Numbers
WHERE
number = POWER(COALESCE(SUBSTRING(CAST(number AS VARCHAR(10)),1,1),0),3)
+ POWER(COALESCE(SUBSTRING(CAST(number AS VARCHAR(10)),2,1),0),3)
+ POWER(COALESCE(SUBSTRING(CAST(number AS VARCHAR(10)),3,1),0),3)
OPTION(MAXRECURSION 0)