OFFSET
1,1
EXAMPLE
n=10: 4n=40 arises as a peak-term in 3x+1 trajectory started at 13, so a[10]=13 and 13 is the least initial value including 40 as a max-term.
MATHEMATICA
c[x_] := (1-Mod[x, 2])*(x/2)+Mod[x, 2]*(3*x+1); c[1]=1; fpl[x_] := Max[Delete[FixedPointList[c, x], -1]] t=Table[fpl[w], {w, 1, 15000}]; Table[Min[Flatten[Position[t, 4*j]]], {j, 1, 256}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Sep 11 2003
STATUS
approved