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Puzzles/Easy Sequence 2/Solution
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Add 1 2 3 4... OR x(x-1)/2+1 :
1 2 4 7 11 16 22 29 ...
:
1 2 4 7 12 20 33 ...
Add the three previous numbers:
1 2 4 7 13 24 44 ...
The numbers with an odd number of ones in their binary representation:
1 2 4 7 8 11 13 ... or 1 10 100 111 1000 1011 1101 ...
A formula for the th number is:
, , .