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.
%I A091703 #32 Nov 20 2022 01:53:42
%S A091703 0,1,2,3,4,0,6,7,8,9,0,11,12,13,14,0,16,17,18,19,0,21,22,23,24,0,26,
%T A091703 27,28,29,0,31,32,33,34,0,36,37,38,39,0,41,42,43,44,0,46,47,48,49,0,
%U A091703 51,52,53,54,0,56,57,58,59,0,61,62,63,64,0,66,67,68,69,0,71,72,73,74,0,76,77
%N A091703 Count, setting 5n to zero.
%H A091703 G. C. Greubel, <a href="/A091703/b091703.txt">Table of n, a(n) for n = 0..10000</a>
%H A091703 <a href="/index/Rec#order_10">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,0,0,2,0,0,0,0,-1).
%F A091703 a(n) = Product_{k=0..4} Sum_{j=1..n} e^(2*Pi*ijk/5), i=sqrt(-1).
%F A091703 a(n) = cos(4*Pi*n/5 + 2*Pi/5)*(n*cos(2*Pi*n/5 + Pi/5)/5 + n*sqrt(1/5 - 2*sqrt(5)/25)*sin(2*Pi*n/5 + Pi/5) + n*(1/5 - sqrt(5)/5)) + sin(4*Pi*n/5 + 2*Pi/5)*(n*sqrt(2*sqrt(5)/25 + 1/5)*cos(2*Pi*n/5 + Pi/5) + sqrt(5)*n*sin(2*Pi*n/5 + Pi/5)/5 - n*sqrt(2*sqrt(5)/25 + 2/5)) - n*(sqrt(5)/5 + 1/5)*cos(2*Pi*n/5 + Pi/5) - n*sqrt(2/5 - 2*sqrt(5)/25)*sin(2*Pi*n/5 + Pi/5) + 4*n/5.
%F A091703 a(n) = n^5 mod (5*n). - _Paul Barry_, Apr 13 2005
%F A091703 Multiplicative with a(5^e) = 0, a(p^e) = p^e otherwise. - _Mitch Harris_, Jun 09 2005
%F A091703 From _R. J. Mathar_, Feb 04 2009: (Start)
%F A091703 a(n) = 2*a(n-5) - a(n-10).
%F A091703 G.f.: x*(1 + 2*x + 3*x^2 + 4*x^3 + 4*x^5 + 3*x^6 + 2*x^7 + x^8)/(1-x^5)^2.
%F A091703 a(n) = |A080891(n)|*A001477(n). (End)
%F A091703 From _R. J. Mathar_, Apr 14 2011: (Start)
%F A091703 a(n) = n*A011558(n).
%F A091703 Dirichlet g.f.: (1-5^(1-s))*zeta(s-1). (End)
%F A091703 Sum_{k=1..n} a(k) ~ (2/5) * n^2. - _Amiram Eldar_, Nov 20 2022
%t A091703 Table[If[Divisible[n,5],0,n],{n,0,80}] (* _Harvey P. Dale_, Apr 26 2018 *)
%o A091703 (PARI) a(n) = if (n % 5, n, 0); \\ _Michel Marcus_, Feb 28 2019
%o A091703 (Magma) [(n mod 5 eq 0) select 0 else n: n in [0..80]]; // _G. C. Greubel_, Feb 28 2019
%o A091703 (Sage) [n if not n % 5==0 else 0 for n in range(80)] # _G. C. Greubel_, Feb 28 2019
%Y A091703 Cf. A001477, A011558, A080891, A091684, A011558.
%K A091703 easy,nonn,mult
%O A091703 0,3
%A A091703 _Paul Barry_, Jan 30 2004