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.

User: Peter Andrew

Peter Andrew's wiki page.

Peter Andrew has authored 3 sequences.

A346458 Numbers with hexadecimal representation A, AB, ABC, ..., ABCDEFA, ABCDEFAB, ...

Original entry on oeis.org

10, 171, 2748, 43981, 703710, 11259375, 180150010, 2882400171, 46118402748, 737894443981, 11806311103710, 188900977659375, 3022415642550010, 48358650280800171, 773738404492802748, 12379814471884843981, 198077031550157503710, 3169232504802520059375
Offset: 1

Views

Author

Peter Andrew, Jul 19 2021

Keywords

Links

Crossrefs

Cf. A325911.

Programs

  • Haskell
    a 1 = 10
a n = a (n - 1) * 16 + 10 + (n - 1) `mod` 6

Formula

a(n) = 16*a(n-1) + 10 + ((n - 1) mod 6) with a(1) = 10.
From Stefano Spezia, Jul 19 2021: (Start)
G.f.: x*(10 + 11*x + 12*x^2 + 13*x^3 + 14*x^4 + 15*x^5)/(1 - 16*x - x^6 + 16*x^7).
a(n) = 16*a(n-1) + a(n-6) - 16*a(n-7) for n > 7. (End)

A335650 Numbers that are multiples of 2,3,5, or 7 but not multiples of the product of any combination of 2,3,5, and 7.

Original entry on oeis.org

2, 3, 4, 5, 7, 8, 9, 16, 22, 25, 26, 27, 32, 33, 34, 38, 39, 44, 46, 49, 51, 52, 55, 57, 58, 62, 64, 65, 68, 69, 74, 76, 77, 81, 82, 85, 86, 87, 88, 91, 92, 93, 94, 95, 99, 104, 106, 111, 115, 116, 117, 118, 119, 122, 123, 124, 125, 128, 129, 133, 134, 136, 141, 142
Offset: 1

Views

Author

Peter Andrew, Jun 15 2020

Keywords

Examples

			4 is a term because 4 = 2 * 2;
77 is a term because 77 = 7 * 11;
6 is not a term because 6 = 2 * 3;
21 is not a term because 21 = 3 * 7;
30 is not a term because 30 = 2 * 3 * 5;
210 is not a term because 210 = 2 * 3 * 5 * 7.

Crossrefs

Cf. A126590.

Programs

  • Haskell
    a335650 = [x | x <- [0..], (gcd x 210) `elem` [2,3,5,7]]
  • Maple
    q:= n-> is(igcd(n, 210) in {2,3,5,7}):
select(q, [$0..200])[];  # Alois P. Heinz, Jun 16 2020
  • Mathematica
    Select[Range[150], Count[IntegerExponent[#, {2, 3, 5, 7}], 0] == 3 &] (* Amiram Eldar, Jun 16 2020 *)

A329004 a(n) is the largest index in [n] that maximizes tau.

Original entry on oeis.org

1, 2, 3, 4, 4, 6, 6, 8, 8, 10, 10, 12, 12, 12, 12, 12, 12, 18, 18, 20, 20, 20, 20, 24, 24, 24, 24, 24, 24, 30, 30, 30, 30, 30, 30, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 72
Offset: 1

Views

Author

Peter Andrew, Jun 10 2020

Keywords

Links

Crossrefs

Cf. A000005, A067128.

Programs

  • Haskell
    a329004 = map fst $ scanl1 (\x y -> maximumBy (comparing snd) [x,y]) $ zip [1..] a000005
  • Maple
    a:= proc(n) option remember; uses numtheory; `if`(n=1, 1,
      (t-> `if`(tau(n)Alois P. Heinz, Jun 11 2020
  • Mathematica
    dmax = 0; nmax = 1; seq = {}; Do[If[(d = DivisorSigma[0, n]) >= dmax, dmax = d; nmax = n]; AppendTo[seq, nmax], {n, 1, 72}]; seq (* Amiram Eldar, Jun 11 2020 *)

Formula

a(n) = n <=> n in { A067128 }. - Alois P. Heinz, Jun 11 2020

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

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