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 A190338 Consider the iteration k -> 3*k mod 10^(number of decimal digits in n). Sequence gives the number of times the iteration has to be applied to n before returning to n. 1
 1, 4, 4, 4, 4, 1, 4, 4, 4, 4, 4, 20, 20, 20, 20, 4, 20, 20, 20, 20, 4, 20, 20, 20, 20, 2, 20, 20, 20, 20, 4, 20, 20, 20, 20, 4, 20, 20, 20, 20, 4, 20, 20, 20, 20, 4, 20, 20, 20, 20, 1, 20, 20, 20, 20, 4, 20, 20, 20, 20, 4, 20, 20, 20, 20, 4, 20, 20, 20, 20 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Pickover called a sequence of this type an "Odin sequence". It seems that a(n) = 4*5^(A055642(n) - 1) whenever n mod 5 <> 0. REFERENCES Clifford A. Pickover, A Passion for Mathematics, Wiley, 2005; see p. 124. LINKS Nathaniel Johnston, Table of n, a(n) for n = 0..10000 MAPLE a := proc(n) local c, k: c:=0:k:=n: do k:=3*k mod (10^length(n)):c:=c+1: if(k=n)then return c: fi: od: end: seq(a(n), n=0..150); MATHEMATICA Flatten[Table[Position[NestList[Mod[3#, 10^IntegerLength[n]]&, n, 40], n][[2]]-1, {n, 0, 70}]] (* Harvey P. Dale, Mar 05 2013 *) CROSSREFS Cf. A055642. Sequence in context: A171408 A071907 A172369 * A199177 A074803 A177229 Adjacent sequences:  A190335 A190336 A190337 * A190339 A190340 A190341 KEYWORD nonn,easy,base AUTHOR Nathaniel Johnston, May 09 2011 STATUS approved

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