Hi, I am new to all this and would love to learn more about card tricks.

Over the weekend I was shown a card trick but my neighbour who did it on me would not reveal how it was done. I have trawled the internet and cannot find it and I'm hoping someone on here can help. The trick is as follows and can be done with any number of card decks put together:

I was sat next to him whilst his family was in the other room. His wife shuffled the cards and then turned the top one over revealing a number card. Say it was number seven. She then proceeded to count the cards from the top of the pack from number seven up to the number 12, so there were six cards in the pack. My friend didn't know the number of cards in the pack. She then turned over another card, say the number was four. She then counted the cards up to the number twelve. This went on until she could not create a pile from the remaining cards to make up to the number twelve. So, for example, from one pack of cards, she had say, seven piles with four left over. All this time, my neighbour was in a separate room sat next to me. When she had finished she shouted to him for example seven piles and four left over. She then turned each pile over to reveal the first card of each pile and added them up. Without any other communication, my neighbour sat next to me correctly revealed the total of the first cards added together. This worked EVERY time and no matter how many times we tried to figure it out, we couldn't. He didn't need to use pen paper to calculate. Apparently, the number thirteen has something to do with it.

He could do the trick over the phone and still get it right.

Has anyone heard/seen this trick before? If so, how do you do it? I don't even know what the trick is called. Please help.

Thanks