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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

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

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.

MATHEMATICA

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

CROSSREFS

Cf. 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 August 17 13:03 EDT 2017. Contains 290635 sequences.