Nth Prime Number

This function returns the nth prime...

create function dbo.F_NTH_PRIME(@n bigint) returns bigint as
begin
declare @MaxNumber bigint, @i bigint
set @MaxNumber = case when @n <=6 then 20 else @n * log(@n) + @n * log(log(@n)) end

declare @t table (n bigint identity(1, 1), i bigint)
insert @t select i from dbo.F_TABLE_PRIME(@MaxNumber)
select @i = i from @t where n = @n

return @i
end

--calculation (ran in 2 seconds for me)
select n, dbo.F_NTH_PRIME(n) as 'nth prime' from (
select 1 n union select 2 union select 3 union select 10 union
select 25 union select 100 union select 1000 union select 9593 union select 10000) a

/*results
n nth prime
----------- --------------------
1 2
2 3
3 5
10 29
25 97
100 541
1000 7919
9593 100003
10000 104729
*/For dbo.F_TABLE_PRIME, see http://www.sqlteam.com/forums/topic.asp?TOPIC_ID=69646


Ryan Randall
www.monsoonmalabar.com London-based IT consultancy

Solutions are easy. Understanding the problem, now, that's the hard part.