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

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, 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, 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

Offset: 1

Author

Vincenzo Librandi, Jun 07 2011

Keywords

• nonn
• easy

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A002808.

Programs

Magma

[IsPrime(n) select 0 else n: n in [1..100]]; // Vincenzo Librandi, May 17 2014

Maple

A191558 := proc(n) if isprime(n) then 0; else n; end if; end proc:
seq(A191558(n),n=1..80) ; # R. J. Mathar, Jun 11 2011

Mathematica

Table[If[PrimeQ[n], 0, n], {n, 150}] (* Vincenzo Librandi, May 17 2014 *)
(*recurrence*)
Clear[t];
nn = 94;
t[1, 1] = 1;
t[n_, k_] :=
  t[n, k] =
   If[n == k, n*(1 - Product[t[n, k - i], {i, 1, k - 1}]),
    If[n > k, t[n - k, k], 1]];
Table[t[n, n], {n, 1, nn}](* Mats Granvik, Jul 05 2014 *)
Table[n (1 - PrimePi[n] + PrimePi[n - 1]), {n, 50}] (* Wesley Ivan Hurt, Jul 06 2014 *)

Formula

a(n) = n * A005171(n) = n - A061397(n). - R. J. Mathar, Jun 11 2011