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A003621
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Number of iterations until n reaches 1 or 4 under x goes to sum of squares of digits map.
(Formerly M4764)
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13
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0, 1, 11, 0, 8, 13, 5, 9, 10, 1, 2, 9, 2, 10, 10, 7, 9, 9, 4, 1, 9, 10, 3, 2, 7, 9, 10, 3, 6, 11, 2, 3, 10, 8, 9, 12, 6, 7, 11, 8, 10, 2, 8, 4, 11, 8, 9, 10, 4, 8, 10, 7, 9, 11, 9, 8, 10, 5, 8, 13, 7, 9, 12, 8, 8, 11, 6, 2, 12, 5, 9, 10, 6, 9, 10, 6, 5, 4, 3, 9
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OFFSET
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1,3
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REFERENCES
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J. Roberts, Lure of the Integers, Math. Assoc. America, 1992, p. 13.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
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FORMULA
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MAPLE
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f:= n -> convert(map(t -> t^2, convert(n, base, 10)), `+`):
g:= proc(n) option remember;
if n = 1 or n = 4 then 0 else 1 + procname(f(n)) fi
end proc:
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MATHEMATICA
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Table[Length[NestWhileList[Total[IntegerDigits[#]^2]&, n, #!=1&&#!=4&]], {n, 80}]-1 (* Harvey P. Dale, Dec 31 2016 *)
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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STATUS
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approved
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