A371183 Lexicographically earliest sequence of distinct terms in which every triple of consecutive digits contains only one pair that is not coprime.

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, 51, 50, 16, 27, 28, 18, 29, 32, 33, 19, 34, 38, 39, 42, 52, 41, 40, 100, 102, 103, 104, 105, 106, 107, 108, 109, 130, 120, 122, 54, 43, 35, 36, 53, 37, 62, 55, 44, 56, 45, 46, 58, 47, 48

Offset

1,2

Links

Table of n, a(n) for n=1..70.

Mathematica

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;
a[n_]:=a[n]=Module[{k=1, digits, tab=Table[a[i], {i, 1, n-1}]},
While[digits=Join[Take[Flatten[IntegerDigits[Take[tab, -3]]], -3], IntegerDigits[k]];
MemberQ[tab, k]||Union[pairwiseQ@@@
Table[{digits[[i]], digits[[i+1]], digits[[i+2]]},
{i, 1, Length[digits]-2}]]!={True}, k++]; k]; a/@Range[70]

Crossrefs

Cf. A353187, A371060, A371182.

Sequence in context: A279356 A241909 A245451 * A368258 A368264 A026166

Adjacent sequences: A371180 A371181 A371182 * A371184 A371185 A371186

Keyword

nonn,base

Author

Ivan N. Ianakiev, Mar 14 2024

Status

approved