last missing number

[excelNewbie22]

hi,
how can i tell the last one missing number from a fixed range, say 1 to 42, without knowing the range of rows? (only from where to check=starting point, like o2:t _)
see example below

test
	O	P	Q	R	S	T	U
1							last missing number
2	1	2	3	4	5	6
3	7	8	9	10	11	12
4	13	14	15	16	17	18
5	19	20	21	22	23	24
6	25	26	27	28	29	30
7	31	32	33	34	35	36
8	1	37	38	39	40	41	42
9	25	26	27	28	29	30
10
11
12	1	2	3	4	5	6
13	7	8	9	10	11	12
14	13	14	15	16	17	18
15	19	20	21	22	23	24
16	25	26	27	28	29	30
17	31	32	33	34	35	36
18	2	7	9	11	13	15
19	35	37	39	40	41	42	38
20	13	14	15	16	17	18
21
22
23	2	3	4	5	6	7
24	7	8	9	10	11	12
25	13	14	15	16	17	18
26	19	20	21	22	23	24
27	25	26	27	28	29	30
28	31	32	33	34	35	36
29	37	38	39	40	41	42
30	5	7	11	22	25	35
31	5	8	9	10	11	12
32	10	12	13	22	23	24	1
33	19	20	21	22	23	24
34	25	26	27	28	29	30
35	31	32	33	34	35	36
test

 

[excelNewbie22]

re-check, all good,
thank you very much!