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 A003621 Number of iterations until n reaches 1 or 4 under x goes to sum of squares of digits map. (Formerly M4764) 13
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 REFERENCES 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). LINKS Seiichi Manyama, Table of n, a(n) for n = 1..10000 (terms 1..1000 from Harvey P. Dale) A. Porges, A set of eight numbers, Amer. Math. Monthly, 52 (1945), 379-382. [Annotated scanned copy] Arthur Porges, A set of eight numbers, Amer. Math. Monthly 52 (1945), 379-382. FORMULA a(n) = 0 if n = 1 or 4, otherwise a(n) = 1 + a(A003132(n)). - Robert Israel, Apr 11 2019 MAPLE 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: map(g, [\$1..100]); # Robert Israel, Apr 11 2019 MATHEMATICA Table[Length[NestWhileList[Total[IntegerDigits[#]^2]&, n, #!=1&&#!=4&]], {n, 80}]-1 (* Harvey P. Dale, Dec 31 2016 *) CROSSREFS Cf. A000216, A000218, A300081, etc. Cf. A003132. Sequence in context: A115595 A342123 A187553 * A348006 A338827 A055963 Adjacent sequences: A003618 A003619 A003620 * A003622 A003623 A003624 KEYWORD nonn,base AUTHOR N. J. A. Sloane, Mira Bernstein STATUS approved

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Last modified June 17 15:39 EDT 2024. Contains 373458 sequences. (Running on oeis4.)