A371183 - OEIS

%I #7 Mar 23 2024 20:30:58

%S 1,2,4,3,8,9,22,5,6,21,20,10,7,17,71,70,12,23,24,14,25,26,13,31,30,15,

%T 51,50,16,27,28,18,29,32,33,19,34,38,39,42,52,41,40,100,102,103,104,

%U 105,106,107,108,109,130,120,122,54,43,35,36,53,37,62,55,44,56,45,46,58,47,48

%N Lexicographically earliest sequence of distinct terms in which every triple of consecutive digits contains only one pair that is not coprime.

%t pairwiseQ[a_,b_,c_]:=Sort[{CoprimeQ[a,b],CoprimeQ[b,c],CoprimeQ[a,c]}]=={False,True,True}; a[1]=1;a[2]=2;a[3]=4;

%t a[n_]:=a[n]=Module[{k=1,digits,tab=Table[a[i],{i,1,n-1}]},

%t While[digits=Join[Take[Flatten[IntegerDigits[Take[tab,-3]]],-3],IntegerDigits[k]];

%t MemberQ[tab,k]||Union[pairwiseQ@@@

%t Table[{digits[[i]],digits[[i+1]],digits[[i+2]]},

%t {i,1,Length[digits]-2}]]!={True},k++];k]; a/@Range[70]

%Y Cf. A353187, A371060, A371182.

%K nonn,base

%O 1,2

%A _Ivan N. Ianakiev_, Mar 14 2024