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A000221 Take sum of squares of digits of previous term. 14
5, 25, 29, 85, 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, 16, 37, 58, 89, 145 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Essentially the same as A080709. - M. F. Hasler, May 24 2009

REFERENCES

R. Honsberger, Ingenuity in Math., Random House, 1970, p. 83.

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

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

Ultimately periodic with period 8.

a(n)=A080709(n) for n>4. - M. F. Hasler, May 24 2009

a(n+1) = A003132(a(n)). - Reinhard Zumkeller, Dec 19 2011

MATHEMATICA

NestList[Plus @@ IntegerDigits[ # ]^2 &, 5, 50]

PROG

(PARI) A000221(n)=[5, 25, 29, 85, 89, 145, 42, 20, 4, 16, 37, 58][n%8+(n%8<5 & n>7)*8] \\ M. F. Hasler, May 24 2009

(MAGMA) [5, 25, 29, 85] cat &cat[[89, 145, 42, 20, 4, 16, 37, 58]: n in [0..17]]; // Vincenzo Librandi, Jan 29 2013

(Haskell)

a000221 n = a000221_list !! (n-1)

a000221_list = iterate a003132 5

-- Reinhard Zumkeller, Mar 04 2013

CROSSREFS

Cf. A003132 (the iterated map), A003621, A039943, A099645, A031176, A007770, A000216 (starting with 2), A000218 (starting with 3), A080709 (starting with 4), A008460 (starting with 6), A008462 (starting with 8), A008463 (starting with 9), A139566 (starting with 15), A122065 (starting with 74169). - M. F. Hasler, May 24 2009

Sequence in context: A070380 A068574 A000350 * A018612 A036127 A018639

Adjacent sequences:  A000218 A000219 A000220 * A000222 A000223 A000224

KEYWORD

nonn,base,easy,nice

AUTHOR

N. J. A. Sloane

STATUS

approved

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Last modified September 24 18:54 EDT 2017. Contains 292433 sequences.