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A033491
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a(n) is the smallest integer that takes n halving and tripling steps to reach 1 in the 3x+1 problem.
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9
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1, 2, 4, 8, 16, 5, 10, 3, 6, 12, 24, 48, 17, 34, 11, 22, 7, 14, 28, 9, 18, 36, 72, 25, 49, 98, 33, 65, 130, 43, 86, 172, 57, 114, 39, 78, 153, 305, 105, 203, 406, 135, 270, 540, 185, 361, 123, 246, 481, 169, 329, 641, 219, 427, 159, 295, 569, 1138, 379, 758, 283, 505
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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LINKS
| T. D. Noe, Table of n, a(n) for n=0..1924 (from Eric Roosendaal's data)
Eric Roosendaal, 3x+1 Class Records
Eric Weisstein's World of Mathematics, Link to a section of The World of Mathematics
Index entries for sequences related to 3x+1 (or Collatz) problem
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MATHEMATICA
| f[ n_ ] := Module[ {i = 0, m = n}, While[ m != 1, m = If[ OddQ[ m ], 3m + 1, m/2 ]; i++ ]; i ]; a = Table[ 0, {75} ]; Do[ m = f[ n ]; If[ a[ [ m + 1 ] ] == 0, a[ [ m + 1 ] ] = n ] ], {n, 1, 1250} ]; a
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PROG
| (PARI) a(n)=if(n<0, 0, k=1; while(abs(if(k<0, 0, s=k; c=1; while((1-(s%2))*s/2+(s%2)*(3*s+1)>1, s=(1-(s%2))*s/2+(s%2)*(3*s+1); c++); c)-n-1)>0, k++); k)
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CROSSREFS
| Cf. A126727 (missing numbers).
Sequence in context: A101943 A110001 A167426 * A050076 A070337 A178170
Adjacent sequences: A033488 A033489 A033490 * A033492 A033493 A033494
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KEYWORD
| nonn,nice
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AUTHOR
| Jeff Burch (gburch(AT)erols.com)
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EXTENSIONS
| More terms from Larry Reeves (larryr(AT)acm.org), Apr 27 2001
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