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.

A387523 Primes in the order in which they first divide a term of A386482.

Original entry on oeis.org

2, 3, 5, 7, 13, 11, 17, 19, 23, 29, 31, 43, 41, 37, 47, 67, 61, 59, 53, 73, 71, 83, 79, 113, 109, 107, 103, 101, 97, 89, 127, 157, 151, 149, 139, 137, 131, 193, 191, 181, 179, 173, 167, 163, 199, 197, 211, 251, 241, 239, 233, 229, 227, 223, 313, 311, 307, 293, 283, 281, 277, 271, 269, 263, 257, 337, 331, 317, 467, 463, 461, 457
Offset: 1

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Author

N. J. A. Sloane, Sep 03 2025

Keywords

Comments

Conjecture: if c is the first term in A386482 that is divisible by a prime p > 2, then c = 2*p.

Examples

			11 first divides A386482(23), but 13 first divides A386482(21), so 13 precedes 11 in this sequence.

Links

Crossrefs

Cf. A386482, A386483, A387072, A387076, A387077, A387522, A387524.

Programs

  • Mathematica
    Block[{p, s}, p[A386482/b386482.txt%22,%20%22Data%22%5D%5B%5BAll,%20-1%5D%5D;%20Rest@%20Reap%5BDo%5BMap%5BIf%5Bp%5B%23%5D%20==%200,%20Set%5Bp%5B%23%5D,%20n%5D;%20Sow%5B%23%5D%5D%20&,%20FactorInteger%5Bs%5B%5Bn%5D%5D%20%5D%5B%5B;;%20,%201%5D%5D%5D,%20%7Bn,%20Length%5Bs%5D%7D%5D%20%5D%5B%5B-1,%201%5D%5D%20%5D%20(*%20_Michael%20De%20Vlieger">] := 0; s = Import["https://oeis.org/A386482/b386482.txt", "Data"][[All, -1]]; Rest@ Reap[Do[Map[If[p[#] == 0, Set[p[#], n]; Sow[#]] &, FactorInteger[s[[n]] ][[;; , 1]]], {n, Length[s]}] ][[-1, 1]] ] (* _Michael De Vlieger, Sep 03 2025 *)

A387524 Primes p with property that in A386482 they are immediately preceded by 2*p and immediately followed by 3*p.

Original entry on oeis.org

3, 7, 11, 19, 31, 47, 131, 317, 947, 4327, 48091, 77237, 158489, 237733, 1973087, 3398221, 4409519
Offset: 1

Views

Author

N. J. A. Sloane, Sep 03 2025

Keywords

Comments

This is in marked contrast to the EKG sequence A064413, where all primes > 2 have this property.

Crossrefs

Cf. A064413, A386482, A386483, A387072, A387076, A387077, A387522, A387523.

Extensions

More terms from Michael De Vlieger, Sep 03 2025

A387634 Indices k such that s(k) is a prime p, s(k-1) = 2*p, and s(k+1) = 3*p, where s = A386482.

Original entry on oeis.org

5, 11, 24, 31, 57, 76, 236, 479, 1532, 7652, 82123, 129791, 274542, 419569, 3367328, 7002435, 7690249
Offset: 1

Views

Author

Michael De Vlieger, Sep 04 2025

Keywords

Examples

			Table of n, a(n), with a(n) = k, listing s(k) and its immediate neighbors:
 n  a(n) = k     s(k-1)      s(k)     s(k+1)
--------------------------------------------
 1         5         6         3          9
 2        11        14         7         21
 3        24        22        11         33
 4        31        38        19         57
 5        57        62        31         93
 6        76        94        47        141
 7       236       262       131        393
 8       479       634       317        951
 9      1532      1894       947       2841
10      7652      8654      4327      12981
11     82123     96182     48091     144273
12    129791    154474     77237     231711
13    274542    316978    158489     475467
14    419569    475466    237733     713199
15   3367328   3946174   1973087    5919261
16   7002435   6796442   3398221   10194663
17   7690249   8819038   4409519   13228557

Crossrefs

Cf. A064413, A386482, A386483, A387072, A387076, A387077, A387522, A387523, A387524.

Programs

  • Mathematica
    s = Import["https://oeis.org/A386482/b386482.txt", "Data"][[All, -1]]; m = Length[s]; t = TakeWhile[Import["https://oeis.org/A387077/b387077.txt", "Data"][[All, -1]], # <= m &]; Select[t, #1 == 2 #2 && #3 == 3 #2 & @@ s[[# - 1 ;; # + 1]] &] ]
Showing 1-3 of 3 results.

Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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