%I A000221
%S A000221 5,25,29,85,89,145,42,20,4,16,37,58,89,145,42,20,4,16,37,
%T A000221 58,89,145,42,20,4,16,37,58,89,145,42,20,4,16,37,58,89,145,
%U A000221 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
%N A000221 Take sum of squares of digits of previous term.
%C A000221 Essentially the same as A080709. [From M. F. Hasler (MHasler(AT)univ-ag.fr), 
               May 24 2009]
%D A000221 R. Honsberger, Ingenuity in Math., Random House, 1970, p. 83.
%D A000221 A. Porges, A set of eight numbers, Amer. Math. Monthly, 52 (1945), 379-382.
%F A000221 Periodic with period 8.
%F A000221 a(n)=A080709(n) for n>4 [From M. F. Hasler (MHasler(AT)univ-ag.fr), May 
               24 2009]
%t A000221 NestList[Plus @@ IntegerDigits[ # ]^2 &, 5, 50]
%o A000221 (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 (MHasler(AT)univ-ag.fr), May 24 2009]
%Y A000221 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 (MHasler(AT)univ-ag.fr), May 24 2009]
%Y A000221 Sequence in context: A070380 A068574 A000350 this_sequence A018612 A036127 
               A018639
%Y A000221 Adjacent sequences: A000218 A000219 A000220 this_sequence A000222 A000223 
               A000224
%K A000221 nonn,base,easy,nice
%O A000221 1,1
%A A000221 N. J. A. Sloane (njas(AT)research.att.com).