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A181666
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Odd part of a(n) is of form (4^k-1)/3.
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1
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1, 2, 4, 5, 8, 10, 16, 20, 21, 32, 40, 42, 64, 80, 84, 85, 128, 160, 168, 170, 256, 320, 336, 340, 341, 512, 640, 672, 680, 682, 1024, 1280, 1344, 1360, 1364, 1365, 2048, 2560
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| Also numbers that need at most one (3x+1) operation to reach 1 in the Collatz conjecture.
Also, members of A023758 divisible by 3, divided by 3 (conjectured).
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LINKS
| Index entries for sequences related to 3x+1 (or Collatz) problem
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PROG
| (PARI) for(n=2, 2000, o=3*n/2^valuation(n, 2)+1; b=ispower(o); if(b&&round(sqrtn(o, b/2))==4, print1(n, " ")))
(PARI) for(n=0, 2500, if(prod(k=1, length(binary(n))-1, component(binary(n), k)+1-component(binary(n), k+1))>0&&n%3==0, print1(n/3, ", "))) (conjectured)
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CROSSREFS
| Sequence in context: A191203 A114652 A191288 * A067943 A067937 A003592
Adjacent sequences: A181663 A181664 A181665 * A181667 A181668 A181669
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KEYWORD
| nonn
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AUTHOR
| Ralf Stephan (ralf(AT)ark.in-berlin.de), Nov 18 2010
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