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 A091828 #5 Mar 30 2012 18:39:22 %S A091828 1,0,3,4,5,2,1,4,5,6,7,6,7,8,7,8,9,4,5,6,3,2,5,6,7,8,7,8,9,8,9,10,9, %T A091828 10,11,8,9,10,9,10,11,10,11,12,9,10,11,10,11,12,11,12,13,6,7,8,7,8,9, %U A091828 8,9,10,5,6,7,4,5,6,7,8,9,8,9,10,9,10,11,10,11,12,9,10,11,10,11,12,11,12,13 %N A091828 a(n)=n-2*valuation(A000254(n),3). %F A091828 For n>7 a(3n)=a(n)+2; a(3n+1)=a(n)+3; (3n+2)=a(n)+4 %o A091828 (PARI) a(n)=if(n<2,1,n-2*valuation(n!*sum(i=1,n,1/i),3)) %Y A091828 Cf. A056792. %K A091828 nonn %O A091828 1,3 %A A091828 _Benoit Cloitre_, Mar 09 2004