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A110731
a(n) is the least term of the period of the sequence defined by t(1)=n; t(k) = t(k-1)/sod(t(k-1)) if t(k-1) is a multiple of sod(t(k-1)) or t(k-1)*sod(t(k-1)) otherwise, where sod(m)=A007953(m) is the sum of digits of m.
0
1, 1, 1, 1, 1, 1, 1, 1, 1, 10, 1144, 1, 28, 10, 10, 28, 136, 1, 19, 10, 1, 1144, 7522840, 1, 28, 208, 1, 28, 3016, 10, 217, 28, 1144, 32032, 28, 1, 37, 174813842944, 208, 10, 20653750, 1, 172, 352, 1, 46, 4888, 1, 532, 10, 32032, 28, 424, 1, 55, 5824, 174813842944
OFFSET
1,10
COMMENTS
Even period lengths from 2 to 16 arise for the first time from n equal to 11, 263, 149, 3244, 7339, 6929, 31201, and 47397, respectively. Are periods of odd length greater than 1 possible? - Giovanni Resta, Nov 27 2019
EXAMPLE
Some terms and corresponding sequences:
a(1)=1 1,1,1,(1),...
a(11)=1144 11,22,88,1408,18304,1144,11440,(1144,11440),...
a(14)=10 14,70,10,10,(10),...
a(263)=1374175 263,2893,63646,1591150,72325,(1374175,38476900,1423645300,50844475),...
MATHEMATICA
a[k_] := Block[{aa, w, t, p}, aa[1] = k; aa[n_] := aa[n] = Block[{s = Plus @@ IntegerDigits@ aa[n-1]}, aa[n-1] If[Mod[aa[n-1], s] == 0, 1/s, s]]; w = Array[aa, 50]; While[({t, p} = FindTransientRepeat[w, 2])[[2]] == {}, w = Array[aa, Length[w] + 50]]; Min[p]]; Array[a, 60]; (* Giovanni Resta, Nov 27 2019 *)
CROSSREFS
Sequence in context: A130598 A267595 A266621 * A223119 A233252 A249849
KEYWORD
nonn,base
AUTHOR
Amarnath Murthy, Aug 09 2005
EXTENSIONS
Edited and extended by Giovanni Resta, Nov 27 2019
STATUS
approved