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%I #8 Jun 08 2017 17:43:52
%S 1,1,11,1,8,13,5,9,10,1,2,9,2,10,10,7,9,9,4,1,9,10,3,2,7,9,10,3,6,11,
%T 2,3,10,8,9,12,6,7,11,8,10,2,8,4,11,8,9,10,4,8,10,7,9,11,9,8,10,5,8,
%U 13,7,9,12,8,8,11,6,2,12,5,9,10,6,9,10,6,5,4,3,9,9,3,7,10,5,2,4,14,4,10,4,6,11,4,8,12,3,4,12,1
%N Row lengths of A082381: number of iterations of "sum of digits squared" until 1 or 4 is reached.
%C In the spirit of A082381, the map A003132 ("sum of digits squared") is applied at least once to the initial value n; the sequence gives the number of iterations until 1 or 4 is reached.
%F a(n) = O(log* n).
%t Table[Length[NestWhileList[Total[IntegerDigits[#]^2]&,n,!MemberQ[{1,4},#]&]]-1,{n,100}]/.(0->1) (* _Harvey P. Dale_, Jun 08 2017 *)
%o (PARI) A171250(n)=my(c=0); until( n==4 || n==1, c++; n=norml2(eval(Vec(Str(n))))); c
%Y Cf. A082381, A003132, A082382, A000216 (n=2), A000218 (n=3), A080709 (n=4), A000221 (n=5), A008460 (n=6), A008461 (n=7: ends in 1), A008462 (n=8), A008462 (n=9), A139566 (n=15), A122065 (n=74169), A000012 (n=1).
%K nonn,base
%O 1,3
%A _M. F. Hasler_, Dec 18 2009
%E Formula from _Charles R Greathouse IV_, Aug 02 2010
%E Corrected and extended by _Harvey P. Dale_, Jun 08 2017
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