Here is one with a rCTE. to put it back together you can use FOR XML PATH or SELECT @var = @var + part. i have done one with FOR XML PATH so figured id post one with SELECT @var = @var + part

DECLARE @num BIGINT

set @num= 102995348548092

DECLARE @numstr VARCHAR(100)

SET @numstr = @num

DECLARE @Str VARCHAR(100) = ''

;WITH rCTE(ID,Ch) AS (SELECT 1, SUBSTRING(@numstr,1,1)

UNION ALL

SELECT ID + 1, SUBSTRING(@numstr,ID+1,1)

FROM rCTE

WHERE ID < DATALENGTH(@numstr))

SELECT @Str = @Str + Ch FROM rCTE ORDER BY ID DESC

SELECT @Str