SET NOCOUNT ON;
USE testdb;
GO

WHILE 1 = 1
BEGIN
	SELECT * INTO #T1 FROM dbo.T1 WITH(NOLOCK);
	CREATE NONCLUSTERED INDEX idx_seq_val ON #T1(seq_val);

	IF EXISTS(
		SELECT *
		FROM (SELECT seq_val AS cur,
				(SELECT MIN(seq_val)
				FROM #T1 AS N
				WHERE N.seq_val > C.seq_val) AS nxt
			FROM #T1 AS C) AS D
		WHERE nxt - cur > 1) BREAK;

	DROP TABLE #T1;
END

SELECT *
FROM (SELECT seq_val AS cur,
		(SELECT MIN(seq_val)
			FROM #T1 AS N
			WHERE N.seq_val > C.seq_val) AS nxt
	FROM #T1 AS C) AS D
WHERE nxt - cur > 1;

DROP TABLE #T1;
GO