cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

Showing 1-3 of 3 results.

A365872 The "double commas" sequence, a variant of A121805. See the Comments and Example sections for detailed explanations.

Original entry on oeis.org

1, 25, 127, 271, 295, 403, 471, 499, 691, 725, 841, 877, 1019, 1201, 1223, 1285, 1387, 1529, 1711, 1733, 1795, 1897, 2041, 2065, 2169, 2353, 2417, 2561, 2585, 2689, 2873, 2937, 3083, 3149, 3335, 3441, 3467, 3613, 3679, 3865, 3971, 3997, 4145, 4253, 4321, 4349, 4537, 4685, 4793, 4861, 4889, 5079, 5269
Offset: 1

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Keywords

Comments

The pair of digits adjacent to the comma between two terms forms an integer that is half the difference between the said terms. This is the lexicographically earliest sequence with this property. It will stop at some point, but when?

Examples

			a(1) = 1 and a(2) = 25 are separated by 24 units, and 24 is twice 12 (or 1,2);
a(2) = 25 and a(3) = 127 are separated by 102 units, and 102 is twice 51 (or 5,1);
a(3) = 127 and a(4) = 271 are separated by 144 units, and 144 is twice 72 (or 7,2);
a(4) = 271 and a(5) = 295 are separated by 24 units, and 24 is twice 12 (or 1,2); etc.
		

Crossrefs

Cf. A121805 (the original 2006 sequence), A365873, A365874, A365875.

Programs

  • Mathematica
    a[1]=1;a[n_]:=a[n]=(k=a[n-1];While[2FromDigits@Join[{Mod[a[n-1],10]},{First@IntegerDigits@k}]!=k-a[n-1],k++];k);Array[a,70]

A365873 The "triple commas" sequence, a variant of A121805. See the Comments and Example sections for detailed explanations.

Original entry on oeis.org

1, 43, 136, 325, 487, 718, 985, 1138, 1381, 1414, 1537, 1750, 1753, 1846, 2032, 2098, 2344, 2470, 2476, 2662, 2728, 2974, 3103, 3202, 3271, 3310, 3319, 3598, 3847, 4069, 4351, 4393, 4495, 4657, 4879, 5164, 5299, 5584, 5719, 6007, 6235, 6403, 6511, 6559, 6847, 7078, 7339, 7630, 7651, 7702, 7783, 7894
Offset: 1

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Author

Keywords

Comments

The pair of digits adjacent to the comma between two terms forms an integer that is the third of the difference between the said terms. This is the lexicographically earliest sequence with this property. It will stop at some point, but when?

Examples

			a(1) = 1 and a(2) = 43 are separated by 42 units, and 42 is 3*14 (or 1,4);
a(2) = 43 and a(3) = 136 are separated by 93 units, and 93 is 3*31 (or 3,1);
a(3) = 136 and a(4) = 325 are separated by 189 units, and 189 is 3*63 (or 6,3);
a(4) = 325 and a(5) = 487 are separated by 162 units, and 162 is 3*54 (or 5,4); etc.
		

Crossrefs

Cf. A121805 (the original 2006 sequence), A365872, A365874, A365875.

Programs

  • Mathematica
    a[1]=1;a[n_]:=a[n]=(k=a[n-1];While[3FromDigits@Join[{Mod[a[n-1],10]},{First@IntegerDigits@k}]!=k-a[n-1],k++];k);Array[a,70]

A365875 The "reversed commas" sequence, a variant of A121805. See the Comments and Example sections for detailed explanations.

Original entry on oeis.org

1, 92, 104, 118, 136, 152, 164, 178, 206, 232, 254, 278, 316, 352, 384, 428, 476, 532, 584, 648, 726, 812, 904, 998, 1016, 1032, 1044, 1058, 1076, 1092, 1104, 1118, 1136, 1152, 1164, 1178, 1196, 1212, 1224, 1238, 1256, 1272, 1284, 1298, 1316, 1332, 1344, 1358, 1376, 1392, 1404, 1418, 1436, 1452, 1464
Offset: 1

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Author

Keywords

Comments

The pair of digits adjacent to the comma between two terms forms an integer that is the difference between the said terms, but read backwards. This is the lexicographically earliest sequence with this property, provide the largest next term is always chosen when there is a choice. The sequence ends after 2514 steps with a(2514) = 99952.

Examples

			After a(1) = 1, we have multiple choices for a(2); they are 12, 22, 32, 42, 52, 62, 72, 82 and 92. We keep 92 for a(2) as 92 is the largest term.
a(1) = 1 and a(2) = 92 are separated by 91 units, and 91 is 19 backwards (or 1,9);
a(2) = 92 and a(3) = 104 are separated by 12 units, and 12 is 21 backwards (or 2,1);
a(3) = 104 and a(4) = 118 are separated by 14 units, and 14 is 41 backwards (or 4,1);
a(4) = 118 and a(5) = 136 are separated by 18 units, and 18 is 81 backwards (or 8,1); etc.
The next choices we encountered (keeping the largest term) were after a(8) = 178 -> {196,206}, then after 812 -> {894,904}, 1976 -> {1992,2002}, 3956 -> {3992,4002}, 19984 -> {19998,20008}, 39958 -> {39996,40006}, 49952 -> {49994,50004}, etc.
		

Crossrefs

Cf. A121805 (the original 2006 sequence), A365872, A365873, A365874.

Programs

  • Mathematica
    NestList[(s=#;li=First@*IntegerDigits/@Table[s+10*k+Mod[s,10],{k,9}]-Range@9;
    Last@Table[s+FromDigits@Join[Position[li,0][[c]],{Mod[s,10]}],{c,Length@Position[li,0]}])&,1,2513]
Showing 1-3 of 3 results.