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A173660 Smallest integer not yet present such that [a(n)+a(n+1)] divides the concatenation [a(n),a(n+1)]. 1

%I

%S 1,2,4,5,10,8,14,7,26,13,20,16,17,34,32,12,6,3,24,30,15,18,9,72,27,54,

%T 45,36,63,126,28,35,42,21,56,43,86,136,51,48,40,50,25,74,37,62,31,68,

%U 64,80,19,38,61,122,76,23,46,53,106,92,115,218,109,224,84

%N Smallest integer not yet present such that [a(n)+a(n+1)] divides the concatenation [a(n),a(n+1)].

%D Posting by Eric Angelini to Sequence Fans Mailing List, Sep 21 2010

%H Alois P. Heinz, <a href="/A173660/b173660.txt">Table of n, a(n) for n = 1..10000</a>

%e 1+2 divides 12 -> 12/3=4

%e 2+4 divides 24 -> 24/6=4

%e 4+5 divides 45 -> 45/9=5

%e 5+10 divides 510 -> 510/15=34

%e 10+8 divides 108 -> 108/18=6

%e 8+14 divides 814 -> 814/22=37

%e ...

%p ina:= proc() false end:

%p ina(1):= true: mina:= 2;

%p a:= proc(n) option remember; global mina; local k;

%p if n=1 then 1

%p else for k from mina while ina(k) or

%p irem(parse(cat(a(n-1), k)), a(n-1)+k)<>0 do od;

%p ina(k):= true; while ina(mina) do mina:= mina+1 od;

%p k

%p fi

%p end:

%p seq(a(n), n=1..70); # _Alois P. Heinz_, Sep 30 2011

%K nonn,base

%O 1,2

%A _N. J. A. Sloane_, Nov 24 2010

%E Corrected and extended by _Alois P. Heinz_, Sep 30 2011

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Last modified October 25 13:09 EDT 2021. Contains 348251 sequences. (Running on oeis4.)