Search: id:A000216
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%I A000216
%S A000216 2,4,16,37,58,89,145,42,20,4,16,37,58,89,145,42,20,4,16,37,
%T A000216 58,89,145,42,20,4,16,37,58,89,145,42,20,4,16,37,58,89,145,
%U A000216 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
%N A000216 Take sum of squares of digits of previous term.
%D A000216 R. Honsberger, Ingenuity in Math., Random House, 1970, p. 83.
%D A000216 A. Porges, A set of eight numbers, Amer. Math. Monthly, 52 (1945), 379-382.
%F A000216 Periodic with period 8.
%F A000216 a(n)=(1/224)*{1027*(n mod 8)+3295*[(n+1) mod 8]-1157*[(n+2) mod 8]-457*[(n+3) 
               mod 8]-177*[(n+4) mod 8]-177*[(n+5) mod 8]+75*[(n+6) mod 8]+859*[(n+7) 
               mod 8]}-18*[C(2*n,n) mod 2], with n>=0 [From Paolo P. Lava (ppl(AT)spl.at), 
               Oct 21 2008]
%o A000216 (PARI) A000216(n)=[2, 4, 16, 37, 58, 89, 145, 42, 20][n%8+8*(n%8<2 & 
               n>1)] \\\\ [From M. F. Hasler (MHasler(AT)univ-ag.fr), May 24 2009]
%Y A000216 Cf. A003132 (the iterated map), A003621, A039943, A099645, A031176, A007770, 
               A000218 (starting with 3), A080709 (starting with 4), A000221 (starting 
               with 5), 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 A000216 Sequence in context: A101926 A087965 A074411 this_sequence A110998 A051861 
               A048222
%Y A000216 Adjacent sequences: A000213 A000214 A000215 this_sequence A000217 A000218 
               A000219
%K A000216 nonn,base
%O A000216 1,1
%A A000216 N. J. A. Sloane (njas(AT)research.att.com).

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