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 A209686 For each n, define a sequence of numbers by S(0)=n, S(i) = sum of last three digits of the concatenation S(0)S(1)S(2)...S(i-1); a(n) = smallest m such that S(m) = 11, or -1 if 11 is never reached. 1

%I

%S -1,6,8,14,7,6,13,16,6,7,5,0,3,8,6,13,16,6,7,7,15,11,7,6,13,16,6,7,9,

%T 1,9,15,6,13,16,6,7,12,1,10,4,6,13,16,6,7,9,1,2,4,6,13,16,6,7,5,1,20,

%U 13,-1,13,16,6,7,4,1,12,2,5,3,16,6,7,10,1,3,11,15,6,13,6,7,19,1,14,6,2,7,5,9,7,9,1,12,4,5

%N For each n, define a sequence of numbers by S(0)=n, S(i) = sum of last three digits of the concatenation S(0)S(1)S(2)...S(i-1); a(n) = smallest m such that S(m) = 11, or -1 if 11 is never reached.

%D Eric Angelini, Posting to Math Fun Mailing List, Mar 11 2012.

%e 3->3->6->12->9->12->12->5->8->15->14->10->5->6->11, so a(3)=14.

%e 59->14->14->9->14->14->9->... never reaches 11, so a(59)=-1.

%Y Cf. A209674.

%K sign,base

%O 0,2

%A _N. J. A. Sloane_, Mar 11 2012

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Last modified July 23 22:47 EDT 2019. Contains 325278 sequences. (Running on oeis4.)