A122065 - OEIS

A122065

Take sum of squares of digits of previous term; start with 74169.

74169, 183, 74, 65, 61, 37, 58, 89, 145, 42, 20, 4, 16, 37, 58, 89, 145, 42, 20, 4, 16, 37, 58, 89, 145, 42, 20, 4, 16, 37, 58, 89, 145, 42, 20, 4, 16, 37, 58, 89, 145, 42, 20, 4, 16, 37, 58, 89, 145, 42, 20, 4, 16, 37, 58, 89, 145, 42, 20, 4, 16, 37, 58, 89, 145, 42, 20, 4

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OFFSET

1,1

COMMENTS

From a quiz, cf. Russel & Carter reference.

REFERENCES

K. Russell and P. Carter, Number Puzzles, W. Foulsham and Co. Ltd. (1993).

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..100

Index entries for linear recurrences with constant coefficients, signature (0, 0, 0, 0, 0, 0, 0, 1).

FORMULA

a(n) = A000218(n) for n >= 4, a(n) = A000216(n-2) for n >= 6. - M. F. Hasler, Apr 27 2018

MATHEMATICA

NestList[Total[IntegerDigits[#]^2]&, 74169, 80] (* Vincenzo Librandi, Jan 29 2013 *)

PROG

(Magma) [74169, 183, 74, 65, 61] cat &cat[[37, 58, 89, 145, 42, 20, 4, 16]: n in [0..17]]; // Vincenzo Librandi, Jan 29 2013

(PARI) A122065_vec=vector(50, n, t=if(n>1, norml2(digits(t)), 74169));

A122065(n)=A122065_vec[n%8+(n>7)*8] \\ M. F. Hasler, Apr 27 2018

CROSSREFS

Cf. A000216 (main entry for related sequences), A003132 (the iterated "sum digits squared" map).

Sequence in context: A256731 A186835 A239587 * A079543 A033450 A033448

Adjacent sequences: A122062 A122063 A122064 * A122066 A122067 A122068

KEYWORD

nonn,base,easy

AUTHOR

Herman Jamke (hermanjamke(AT)fastmail.fm), Sep 14 2006

STATUS

approved