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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)
12
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

A. Porges, A set of eight numbers, Amer. Math. Monthly, 52 (1945), 379-382.

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

Harvey P. Dale, Table of n, a(n) for n = 1..1000

MATHEMATICA

Table[Length[NestWhileList[Total[IntegerDigits[#]^2]&, n, #!=1&&#!=4&]], {n, 80}]-1 (* Harvey P. Dale, Dec 31 2016 *)

CROSSREFS

A000216, A000218, etc.

Sequence in context: A173189 A115595 A187553 * A055963 A127805 A256480

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 May 29 17:00 EDT 2017. Contains 287253 sequences.