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 A120067 Swap each two consecutive semiprimes. 0
 1, 2, 3, 6, 5, 4, 7, 8, 10, 9, 11, 12, 13, 15, 14, 16, 17, 18, 19, 20, 22, 21, 23, 24, 26, 25, 27, 28, 29, 30, 31, 32, 34, 33, 38, 36, 37, 35, 46, 40, 41, 42, 43, 44, 45, 39, 47, 48, 51, 50, 49, 52, 53, 54, 57, 56, 55, 62, 59, 60, 61, 58, 63, 64, 69, 66, 67, 68, 65, 70, 71, 72 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS EXAMPLE Start with the sequence of natural numbers: 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20, First pair of consecutive semiprimes are 4 and 6, swap them: 1,2,3,6,5,4,7,8,9,10,11,12,13,14,15,16,17,18,19,20, next pair of consecutive semiprimes are 9 and 10, swap them: 1,2,3,6,5,4,7,8,10,9,11,12,13,14,15,16,17,18,19,20, next pair of consecutive semiprimes are 14 and 15, swap them: 1,2,3,6,5,4,7,8,10,9,11,12,13,15,14,16,17,18,19,20, etc. MATHEMATICA s=Range@200; sp=Select[s, 2==Total[Last/@FactorInteger[ # ]]&]; Do[a=sp[[i]]; b=sp[[i+1]]; s[[a]]=b; s[[b]]=a, {i, 1, 61, 2}]; s CROSSREFS Sequence in context: A222241 A056023 A133259 * A089843 A269378 A131145 Adjacent sequences:  A120064 A120065 A120066 * A120068 A120069 A120070 KEYWORD nonn AUTHOR Zak Seidov, Jun 07 2006 STATUS approved

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Last modified August 3 10:49 EDT 2020. Contains 336198 sequences. (Running on oeis4.)