Psalm 136 comprises 26 verses, each ending with
For His mercy endures forever.
Our pastor stated this morning that 26 was a special number in this regard, but didn't clarify this. Now 26 is of course the number of letters in the Latin alphabet, but that didn't exist when the Psalm was written (Psalm 119 is a well-known acrostic but it uses 22 letters, not 26). If you subtract 2, you get twice the number of tribes, but that's a little far-fetched if you ask me.
Searching on Google didn't yield any meaningful results, and most lists of numbers in the Bible like this one don't include 26. Is there any deeper meaning behind this number, or is it just a wonderful song of praise that happens to be 26 verses long?