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 A109013 #22 Oct 18 2019 03:59:25 %S A109013 10,1,2,1,2,5,2,1,2,1,10,1,2,1,2,5,2,1,2,1,10,1,2,1,2,5,2,1,2,1,10,1, %T A109013 2,1,2,5,2,1,2,1,10,1,2,1,2,5,2,1,2,1,10,1,2,1,2,5,2,1,2,1,10,1,2,1,2, %U A109013 5,2,1,2,1,10,1,2,1,2,5,2,1,2,1,10,1,2,1,2,5,2,1,2,1,10,1,2,1,2,5,2,1 %N A109013 a(n) = gcd(n,10). %F A109013 a(n) = 1 + [2|n] + 4*[5|n] + 4*[10|n], where [x|y] = 1 when x divides y, 0 otherwise. %F A109013 a(n) = a(n-10). %F A109013 Multiplicative with a(p^e, 10) = gcd(p^e, 10). - _David W. Wilson_, Jun 12 2005 %F A109013 G.f.: ( -10 - x - 2*x^2 - x^3 - 2*x^4 - 5*x^5 - 2*x^6 - x^7 - 2*x^8 - x^9 ) / ( (x-1)*(1+x)*(x^4 + x^3 + x^2 + x + 1)*(x^4 - x^3 + x^2 - x+1) ). - _R. J. Mathar_, Apr 04 2011 %F A109013 Dirichlet g.f.: zeta(s)*(1 + 1/2^s + 4/5^s + 4/10^s). - _R. J. Mathar_, Apr 04 2011 %F A109013 a(n) = ((n-1) mod 2 + 1)*(4*floor(((n-1) mod 5)/4) + 1). - _Gary Detlefs_, Dec 28 2011 %t A109013 GCD[Range[0,100],10] (* _Harvey P. Dale_, Jul 11 2011 *) %Y A109013 Cf. A109004. %K A109013 nonn,easy,mult %O A109013 0,1 %A A109013 _Mitch Harris_