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April 11th, 2017, 01:15 AM  #1 
Newbie Joined: Apr 2016 From: England Posts: 13 Thanks: 2  Working out numbers which are in both sequences.
This question's really stumped me, and I can't seem to find any tutorials on how to answer it... The nth term of a sequence is 2n + 1 The nth term of a different sequence is 3n 1 Work out the three numbers that are in both sequences and between 20 and 40 Now the three numbers I managed to get are 25, 31 and 37 (as I assumed it meant the output of both of these sequences needs to be the same as well as being in between 20 and 40). For example 2x18+1= 37 as does 3x12+1= 37. Yet I still feel I'm going the wrong way around this. Many thanks in advance Last edited by skipjack; April 11th, 2017 at 03:05 AM. 
April 11th, 2017, 01:45 AM  #2  
Senior Member Joined: Sep 2015 From: CA Posts: 1,265 Thanks: 650  Quote:
$3n+1$ will be odd for $n$ even the numbers with even index in the 2nd sequence between 20 and 40 are 25,31,37 as you discovered. Last edited by skipjack; April 11th, 2017 at 03:06 AM.  

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