I am looking for a mathematical effect that appears as the first effect on one of the Penguin Lectures and I cannot for the life of me remember whose it was.

It starts off with a column of numbers (three to five digits, I think) written to the left and the spectator is asked to choose some of them to establish new sets of numbers, which are then written on the right. Those new numbers are then added up to total whatever you want: a birthday, the date (as in today, 200925), etc. There was a way to work backwards from the desired total to get the numbers that would be needed to get to that total, but the lecturer also had a friend work up a simple (and free) online calculator that would do the work for you instantly.

Thanks in advance if anyone knows what I'm talking about.

I think it was a lecture of Jan Forster. You might need to check my spelling.

It was Marc Paul's first Penguin Lecture if I'm not mistaken.

I aggree.

Marc Paul! That's it! Thanks so much Mr. Mindbender and hcs. I really appreciate it.

I haven't seen the Mark Paul lecture (is it good?), but there was something somewhat similar in Dan Harlan's first Penguin Live Lecture, with a number arrived at by handing out numbered Uno cards and having them arranged by three participants before being summed up.

Mark Paul's handling is more spophisticated.

Thanks! I'll keep that one in mind the next time I'm shopping for lectures.

His tip to use post-it notes with the numbers is really good. That is the way I do it now (instead of crossing out and re-writing the numbers).

Outstanding effect and a great example of how to quickly establish a character and theme for the show.

I am a huge Marc Paul fan!

The effect as you described is in the Marc Paul Lecture,
There is an impromptu version on the Bob Cassidy lecture called Fetch, Robin, Mulica

An effect with the same basic method but a kind of backwards premise is Richard Osterlinds - Radio Sum Total.
here a sum of 4 or 5 numbers equals to the same number formed on the spot by the audience.

The Jan Forster effect dscanning refers to is caller Hypno numbers I believe.
It is related to the Osterlind effect but adds some extra layers to it, and is in my opinion the most deceptive version.