Hi Manuel

=LOOKUP(99^99,$A$1:A20)+1
would give 5 in A21, with the data that you show.

It is not a formula that can be copied down the column, however, as it
would fill very cell with the next number in the sequence.

Assuming your example is accurate the consecutive numbers are separated by
blanks...
How about using the value of the Next Non-blank cell?

Try this:
Select the range of numbers and blanks
Press the [F5] key......a shortcut for <edit><goto>
Click the [Special] button and Check: Blanks
Click the [OK] button

Next....while the blank cells are selected
Type: =
Press the Down Arrow key 1 time
Hold down the [Ctrl] key and Press [Enter]

That's all.

Example (using part of your posted data)
That method converts this:
1
2
(blank)
(blank)
(blank)
3
(blank)
(blank)
(blank)
4

To this:
1
2
3
3
3
3
4
4
4
4

Is that something you can work with?

***********
Regards,
Ron

XL2002, WinXP

As you can tell by the *completely different* suggestions of Roger and Ron,
your question is not at all clear!

I for one, am completely in the dark, as to what you're looking for.
Care to clarify?