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: Jeffrey Burch

Jeffrey Burch's wiki page.

Jeffrey Burch has authored 2 sequences.

A321067 Considering Pythagorean triple (a,b,c) with a < b < c, least a such that there exists a primitive triple where c - b is the n-th term of A096033.

Original entry on oeis.org

3, 8, 20, 33, 48, 65, 88, 119, 140, 204, 207, 252, 297, 336, 396, 429, 540, 555, 616, 696, 731, 832, 893, 1036, 1113, 1140, 1248, 1311, 1428, 1525, 1692, 1748, 1809, 1960, 2059, 2184, 2325, 2508, 2576, 2739, 2832
Offset: 1

Author

Jeffrey Burch, Oct 26 2018

Keywords

Examples

			a(2) = 8 because in the primitive triple (8,15,17), c - b = A096033(2) = 2 and no smaller a yields a primitive triple where a < b < c and c - b = 2.
		

Crossrefs

Programs

  • Mathematica
    nmax = 100; kmax = 2;
    A096033 = Union[2 Range[nmax]^2, (2 Range[0, Ceiling[nmax/Sqrt[2]]]+1)^2];
    r[n_, k_] := Module[{a, b, c}, {a, b, c} /. {ToRules[Reduce[0 < a < b < c && c - b == A096033[[n]] && a^2 + b^2 == c^2, {a, b, c}, Integers] /. C[1] -> k]}];
    a[n_] := a[n] = SelectFirst[Flatten[Table[r[n, k], {k, 1, kmax}], 1], GCD @@ # == 1 &] // First;
    Table[Print[n, " ", a[n]]; a[n], {n, 1, 100}] (* Jean-François Alcover, Jan 01 2019 *)

A200612 The arithmetic mean of the prime factors (with multiplicity) of n is 3.

Original entry on oeis.org

3, 9, 20, 27, 60, 81, 112, 180, 243, 336, 400, 540, 729, 1008, 1200, 1620, 2187, 2240, 2816, 3024, 3600, 4860, 6561, 6720, 8000, 8448, 9072, 10800, 12544, 13312, 14580, 19683, 20160, 24000, 25344, 27216, 32400, 37632, 39936, 43740, 44800, 56320, 59049, 60480
Offset: 1

Author

Jeffrey Burch, Nov 19 2011

Keywords

Examples

			20 is in the sequence because 20 = 2*2*5 and (2+2+5)/3 = 9/3 = 3.
		

Crossrefs

Subsequence of A078175.

Programs

  • Haskell
    a200612 n = a200612_list !! (n-1)
    a200612_list = filter f [2..] where
       f x = r == 0 && x' == 3 where (x',r) = divMod (a001414 x) (a001222 x)
    -- Reinhard Zumkeller, Nov 20 2011
    
  • Maple
    for i from 2 to 35000 do: a:=ifactors(i): s:=sum((a[2][j][1]*a[2][j][2]),j=1..nops(a[2])): t:=sum((a[2][j][2]),j=1..nops(a[2])): if s/t=3 then print(i); fi od:
  • Mathematica
    Select[Range[61000],Mean[Flatten[Table[#[[1]],{#[[2]]}]&/@FactorInteger[ #]]]==3&] (* Harvey P. Dale, Nov 08 2013 *)
  • PARI
    isok(n) = my(f = factor(n)); (sum(k=1, #f~, f[k,1]*f[k,2]) / vecsum(f[,2])) == 3; \\ Michel Marcus, Feb 22 2016

Formula

A001414(a(n)) mod A001222(a(n)) = 0 and A001414(a(n))/A001222(a(n)) = 3. [Reinhard Zumkeller, Nov 20 2011]