A159560 - OEIS

%I #14 Dec 10 2019 03:59:52

%S 3,4,5,7,10,11,13,16,18,19,20,23,24,26,27,29,33,37,38,39,40,41,44,47,

%T 48,49,50,53,60,61,64,65,68,69,72,73,74,75,76,79,84,89,91,92,93,97,98,

%U 101,104,106,108,109,111,112,115,116,117,121,126,127,129,133,137,141,150

%N Minimal recursive sequence beginning with 3 such that A001221(a(n)) = A001221(n).

%H Amiram Eldar, <a href="/A159560/b159560.txt">Table of n, a(n) for n = 2..10000</a>

%H V. Shevelev, <a href="http://arXiv.org/abs/0904.2101">Several results on sequences which are similar to the positive integers</a>, arXiv:0904.2101 [math.NT], 2009.

%F a(n+1) = min{m > a(n): A001221(m) = A001221(n+1)}.

%p A001221 := proc(n) nops(numtheory[factorset](n)) ; end proc:

%p A159560 := proc(n) option remember; if n = 2 then 3; else for a from procname(n-1)+1 do if A001221(a) = A001221(n) then return a; end if; end do: end if; end proc:

%p seq(A159560(n),n=2..70) ; # _R. J. Mathar_, Oct 30 2010

%t a[2] = 3; a[n_] := a[n] = For[an = a[n - 1] + 1, True, an++, If[PrimeNu[an] == PrimeNu[n], Return[an]]];

%t Table[a[n], {n, 2, 66}] (* _Jean-François Alcover_, Nov 14 2017 *)

%Y Cf. A001221, A159559.

%K nonn

%O 2,1

%A _Vladimir Shevelev_, Apr 15 2009

%E Corrected (4 inserted, 8 removed) and extended beyond 53 by _R. J. Mathar_, Oct 30 2010