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A222617 Number of integers k < n whose Collatz (3x+1) trajectory contains n. 1
0, 0, 0, 1, 1, 0, 0, 4, 0, 4, 2, 0, 3, 1, 0, 11, 4, 0, 0, 9, 0, 5, 1, 0, 0, 9, 0, 2, 2, 0, 1, 1, 0, 11, 5, 0, 0, 2, 0, 25, 1, 0, 0, 6, 0, 5, 3, 0, 1, 1, 0, 23, 9, 0, 0, 3, 0, 7, 1, 0, 6, 3, 0, 2, 2, 0, 2, 1, 0, 14, 7, 0, 0, 4, 0, 7, 1, 0, 0, 19, 0, 2, 2, 0, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,8
COMMENTS
It is assumed that Collatz trajectory ends at 1.
REFERENCES
R. K. Guy, Unsolved Problems in Number Theory, E16.
LINKS
EXAMPLE
a(8)=4, since 8 appears in Collatz trajectories of n < 8; similarly a(9)=0 since 9 does not appear in Collatz trajectories n < 9.
MATHEMATICA
Collatz[n_] := NestWhileList[If[EvenQ[#], #/2, 3 # + 1] &, n, # > 1 &]; nn = 100; t = Table[Collatz[n], {n, nn}]; Table[r = 0; Do[If[MemberQ[t[[i]], k], r++], {i, k - 1}]; r, {k, nn}] (* T. D. Noe, Feb 26 2013 *)
CROSSREFS
Cf. A070165.
Sequence in context: A140574 A010636 A222302 * A204695 A175435 A160214
KEYWORD
nonn
AUTHOR
Jayanta Basu, Feb 26 2013
STATUS
approved

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Last modified March 28 14:38 EDT 2024. Contains 371254 sequences. (Running on oeis4.)