1, 3, 6, 55, 66...
Series teasers are where you try to complete the sequence of a series of letters, numbers or objects.
What are the next three numbers in this series?
1, 3, 6, 55, 66, 171, 595, 666, 3003, 5995, ?, ?, ?
Answer
8778, 15051, 66066
These are the 1st 13 palindromic triangular numbers.
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Comments
swordflame
Dec 02, 2004
 For those people who don't know what a triangular number is, http://mathworld.wolfram.com/TriangularNumber.html is a very nice introduction (helped me anyway). 
Nicky101
Dec 07, 2004
 Thanx, I'll go there 
i_am_hated
Apr 13, 2005
 me too...eventually ^_^ 
Nicholle
Apr 21, 2005
 I still don't get it. 
deadeye823
Apr 26, 2005
 wow...the hardest teaser on the site 
darthforman
May 11, 2005
 it IS the hardest...

KimOHara
May 21, 2005
 I got the triangular part right away, but couldn't get the other part... the EASY part, now that I know what it was! 
lessthanjake789
Jun 01, 2005
 i got the palindromic triangle part, but dont know how to figure out triangle numbers, and wasnt sitting there for a LONG LONG time doing them and checking for palindromicity (yes, i made that word up) 
triskit
Jun 02, 2005
 i didnt get it 
Question_Mark
Jun 11, 2005
 WOW! THAT IS HARD! 
brianz
Jun 11, 2005
 I realized they were all triangular numbers but couldn't figure out the correlation between them.
Nice teaser, I don't think it is so hard. 
LlamaLlover
Sep 22, 2005
 Orangutans forced to watch Days Of Our Lives could have aced that one. Try and think of something harder next time. 
hamburger
Oct 02, 2005
 I got the palindrome part, ( Didnt everyone ) But I didnt see the triangular part right away.This was very hard! 
(user deleted)
Oct 05, 2005
 I learned triangular numbers in year 7 EASY 
schatzy228
Oct 09, 2005
 WOW!, needed 2nd cup of coffee and 40yrs of memory back to high school, but it finally came to me GREAT JOB 
bamfan
Oct 24, 2005
 con grats on the hardest teaser
p.s. did any one get it right 
smarty_blondy
Nov 07, 2005
 Hardest one on site? I got this one right away as i knew half of them and so i got the pattern. Only had to do a bit of googling for the missing ones. I will admit it's brilliant though, good job! 
mrbrainyboy
Dec 06, 2005

don't get it...

trickyone
Jan 02, 2006
 I got tha palindrome part but only got the triangular number part after the hint 
tolkienfan27
May 10, 2006
 
MalcolmReynolds
Oct 12, 2006
 Heh .. I was trying to work out a pattern before I realized they were palindromic.
Lol................. 1,3,6,10,55,66,171
corresonds with 1,2,3,10,11,18...
Okay, maybe it's 123, 123... 1+0=1... 1+1= 2... 1+8=.. damn.
Didn't want to go down the line calculating.. so I googled palindromic triangular numbers 
Dan141
Nov 14, 2006
 Easy, just simple....Not its the hardest one here 
javlad27
Jul 28, 2007
 what's a triangular number?

javaguru
Jan 08, 2009
 Took longer to figure out what the next three palindromic triangular numbers were than it did to figure out the rule.
Pretty nice teaser, but not terribly difficult.

Photon
Mar 09, 2009
 I don't understand why this one is rated so difficult? 
krishnan
Sep 01, 2010
 Nice, fun teaser, got the answer as soon as I saw 55 and 66. 
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