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A000221
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Take sum of squares of digits of previous term.
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13
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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; internal format)
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OFFSET
| 1,1
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COMMENTS
| Essentially the same as A080709. [From M. F. Hasler (www.univ-ag.fr/~mhasler), May 24 2009]
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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.
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FORMULA
| Periodic with period 8.
a(n)=A080709(n) for n>4 [From M. F. Hasler (www.univ-ag.fr/~mhasler), May 24 2009]
a(n+1) = A003132(a(n)). [Reinhard Zumkeller, Dec 19 2011]
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MATHEMATICA
| NestList[Plus @@ IntegerDigits[ # ]^2 &, 5, 50]
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PROG
| (PARI) A000221(n)=[5, 25, 29, 85, 89, 145, 42, 20, 4, 16, 37, 58][n%8+(n%8<5 & n>7)*8] \\\\ [From M. F. Hasler (www.univ-ag.fr/~mhasler), May 24 2009]
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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). [From M. F. Hasler (www.univ-ag.fr/~mhasler), May 24 2009]
Sequence in context: A070380 A068574 A000350 * A018612 A036127 A018639
Adjacent sequences: A000218 A000219 A000220 * A000222 A000223 A000224
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KEYWORD
| nonn,base,easy,nice
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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