Each of the triangular numbers that are below 1000 is written on a separate card. Some of these cards are then placed in a circle so that, viewed from the center, the right-hand digit of each card matches the left-hand digit of the card to its right. No tricks are used such as turning a card upside-down.

What's the maximum number of digits that can appear on such a subset of the cards?

15, 55, 528, 861, 171, 105, 595, 561, 153, 351


Much of what I said in "One Ring" (first  comment here) is pertinent.

I've "upped" my ante to 10 numbers with a total of 28 digits.

Note: While some numbers end in "0" I dismissed them since we couldn't realistically have leading "0's", could we?  Also single digit numbers were ruled out because right-hand/left-hand digits implies at least two digits.

Edited on January 10, 2008, 8:10 am

Posted by brianjn on 2008-01-10 07:44:10