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A191558 a(n) = 0 if n prime, otherwise n.

%I A191558 #25 Sep 08 2022 08:45:57
%S A191558 1,0,0,4,0,6,0,8,9,10,0,12,0,14,15,16,0,18,0,20,21,22,0,24,25,26,27,
%T A191558 28,0,30,0,32,33,34,35,36,0,38,39,40,0,42,0,44,45,46,0,48,49,50,51,52,
%U A191558 0,54,55,56,57,58,0,60,0,62,63,64,65,66,0,68,69,70,0,72,0,74,75,76,77,78,0,80,81,82,0,84,85,86,87,88,0,90,91,92,93,94
%N A191558 a(n) = 0 if n prime, otherwise n.
%H A191558 Vincenzo Librandi, <a href="/A191558/b191558.txt">Table of n, a(n) for n = 1..10000</a>
%F A191558 a(n) = n * A005171(n) = n - A061397(n). - _R. J. Mathar_, Jun 11 2011
%p A191558 A191558 := proc(n) if isprime(n) then 0; else n; end if; end proc:
%p A191558 seq(A191558(n),n=1..80) ; # _R. J. Mathar_, Jun 11 2011
%t A191558 Table[If[PrimeQ[n], 0, n], {n, 150}] (* _Vincenzo Librandi_, May 17 2014 *)
%t A191558 (*recurrence*)
%t A191558 Clear[t];
%t A191558 nn = 94;
%t A191558 t[1, 1] = 1;
%t A191558 t[n_, k_] :=
%t A191558   t[n, k] =
%t A191558    If[n == k, n*(1 - Product[t[n, k - i], {i, 1, k - 1}]),
%t A191558     If[n > k, t[n - k, k], 1]];
%t A191558 Table[t[n, n], {n, 1, nn}](* _Mats Granvik_, Jul 05 2014 *)
%t A191558 Table[n (1 - PrimePi[n] + PrimePi[n - 1]), {n, 50}] (* _Wesley Ivan Hurt_, Jul 06 2014 *)
%o A191558 (Magma) [IsPrime(n) select 0 else n: n in [1..100]]; // _Vincenzo Librandi_, May 17 2014
%Y A191558 Cf. A002808.
%K A191558 nonn,easy
%O A191558 1,4
%A A191558 _Vincenzo Librandi_, Jun 07 2011