Around 1955 Stanislaw Ulam identified the lucky number sequence 1 3 7 9 13 15 21 25 31 33 37 …. Start with the odd numbers 1 3 5 7 9 11 13 15 17 19 21 … and keep 1 in the sequence. The next number is 3; strike out every third number from the beginning so that the sequence is 1 3 7 9 13 15 19 21 …. This strikes out 5 11 17 23 and so on. The ;;
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