3
7
12
?
15
4
67
1
9
5
28
2
1
6
4​

1 thought on “3<br />7<br />12<br />?<br />15<br />4<br />67<br />1<br />9<br />5<br />28<br />2<br />1<br />6<br />4​”

1. Answer:

   2+2=4, 2+3=5, 2+5=7, 2+7=9, 2+11=13, 2+13=15, 2+17=19, 2 +19=21, 2+23=25, 2+29=31, 2+31=33, 2+37=39, 2+41=43, 2+ 43=45, 2+47=49, 2+53=55, 2+59=61, 2+61=63, 2+67=69, …

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