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, 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

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 A320086 A074803

Adjacent sequences: A190335 A190336 A190337 * A190339 A190340 A190341

Keyword

nonn,easy,base

Author

Nathaniel Johnston, May 09 2011

Status

approved