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.

A123581 a(1) = 3, a(n) = a(n-1) + greatest prime factor of a(n-1).

Original entry on oeis.org

3, 6, 9, 12, 15, 20, 25, 30, 35, 42, 49, 56, 63, 70, 77, 88, 99, 110, 121, 132, 143, 156, 169, 182, 195, 208, 221, 238, 255, 272, 289, 306, 323, 342, 361, 380, 399, 418, 437, 460, 483, 506, 529, 552, 575, 598, 621, 644, 667, 696, 725, 754, 783, 812, 841, 870
Offset: 1

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Author

Ben Paul Thurston, Nov 12 2006

Keywords

Examples

			a(16) = 88 because a(15) is 77 whose largest prime factor is 11 so 77 + 11 = 88.
		

Crossrefs

Essentially the same as A036441 and A076271.
Cf. A070229.

Programs

  • Haskell
    a123581 n = a123581_list !! (n-1)
    a123581_list = iterate a070229 3  -- Reinhard Zumkeller, Nov 07 2015
  • Maple
    A123581:= proc(n) option remember;
    local t;
    t:= procname(n-1);
    t + max(numtheory[factorset](t));
    end proc;
    A123581(1):= 3;
    seq(A123581(n),n=1..100); # Robert Israel, May 18 2014
  • Mathematica
    a[1] = 3; a[n_] := a[n] = a[n - 1] + FactorInteger[a[n - 1]][[ -1, 1]]; Array[a, 56] (* Robert G. Wilson v *)
  • PARI
    {print1(a=3,",");for(n=2,57,print1(a=a+vecmax(factor(a)[,1]),","))} \\ Klaus Brockhaus, Nov 19 2006
    

Formula

a(n+1) = A070229(a(n)). - Reinhard Zumkeller, Nov 07 2015

Extensions

More terms from Robert G. Wilson v and Klaus Brockhaus, Nov 18 2006