A371182 Lexicographically earliest strictly increasing sequence of positive integers in which every triple of consecutive digits contains only one pair that is not coprime.

1, 2, 4, 5, 6, 8, 10, 21, 22, 32, 33, 42, 52, 54, 55, 62, 72, 74, 76, 77, 82, 92, 93, 100, 102, 103, 104, 105, 106, 107, 108, 109, 130, 133, 136, 139, 160, 162, 163, 164, 166, 168, 169, 190, 193, 196, 199, 221, 223, 225, 227, 229, 232, 233, 234, 238, 239, 241, 243, 245

Offset

1,2

Links

Table of n, a(n) for n=1..60.

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[4]=5; a[5]=6; a[6]=8; a[7]=10;
a[n_]:=a[n]=Module[{k=a[n-1]+1, digits},
While[digits=Join[Take[IntegerDigits[a[n-1]], -2], IntegerDigits[k]];
Union[ pairwiseQ@@@Table[{digits[[i]], digits[[i+1]], digits[[i+2]]},
{i, 1, Length[digits]-2}]]!={True}, k++]; k]; a/@Range[60]

Crossrefs

Cf. A353187, A371060, A371183.

Sequence in context: A362942 A069872 A216163 * A093080 A059916 A099747

Adjacent sequences: A371179 A371180 A371181 * A371183 A371184 A371185

Keyword

nonn,base

Author

Ivan N. Ianakiev, Mar 14 2024

Status

approved