OFFSET
0,1
COMMENTS
a(40) is the first time the periodic part of the trajectory contains more than one term.
LINKS
Julien Kluge, Table of n, a(n) for n = 0..10000
EXAMPLE
Consider the starting value n = 5. We see one five: 15. We have one ones and one 5: 1115. We have three ones and one five: 3115... We reach 3122331415 which produces itself. So a(5) = 3122331415.
MATHEMATICA
a005151[n_, m_] :=
FromDigits[
Reverse /@
Sort[Tally[
If[n == 2, m, a005151[n - 1, m]] //
IntegerDigits], #1[[1]] < #2[[1]] &] // Flatten];
a[n_] := Block[{previousNum = 0, currentNum = 1, knownNums = {n}},
For[i = 2, currentNum != previousNum, ++i,
previousNum = currentNum;
currentNum = a005151[i, n];
If[MemberQ[knownNums, currentNum], Return[currentNum],
AppendTo[knownNums, currentNum]];
];
Return[currentNum];
]
a /@ Range[0, 100]
CROSSREFS
KEYWORD
nonn,easy,base
AUTHOR
Julien Kluge, Jan 31 2016
STATUS
approved